ChatGPT answers, unedited

If your goal is “someone visits on desktop, then sees relevant retargeting ads on their phone (and vice versa)”, I’d shortlist these:

My recommendation

For most serious advertisers: The Trade Desk + LiveRamp.

The Trade Desk's Identity Alliance combines multiple cross-device identity graphs and can apply frequency caps across a user's devices—not just the device where they originally saw the ad. partner.thetradedesk.com LiveRamp can provide the first-party identity/audience layer and distribute audiences to TTD, DV360, Meta, Amazon and other destinations. docs.liveramp.com

If you're already using Google Analytics/Google Ads: I'd lean toward DV360. Google supports cross-device conversion measurement across desktop web, mobile web and mobile apps, and LiveRamp can feed first-party audiences into DV360. support.google.com

If you're an ecommerce/DTC company: I'd seriously evaluate Criteo alongside TTD/DV360. Its sweet spot is dynamic retargeting—showing someone the products/categories they actually interacted with rather than generic brand ads.

One important distinction

“Cross-device retargeting” can mean two different things:

1. Deterministic: You know the visitor is the same person because they're logged in, provided an email, etc. Best accuracy.
2. Probabilistic/identity-graph: The platform infers that a desktop, phone and tablet belong to the same household/person. More reach, but less certain.

For a modern setup, I'd prioritize first-party login/email signals + consented identity resolution, then use the DSP for activation. Don't rely solely on third-party cookies.

If you tell me your monthly ad spend, B2B vs. ecommerce, and whether you need Meta/Google/CTV as well as the open web, I can narrow this to the 2–3 best platforms and approximate cost/complexity.

If your main goal is “someone visits on mobile, then sees relevant retargeting on desktop (and vice versa)”, I’d shortlist these:

🥇 My pick: Criteo

Criteo is particularly well suited to what you're describing. Its Shopper Graph connects identifiers across devices, and Criteo explicitly supports scenarios where someone browses on mobile and can subsequently be served relevant ads on desktop. www.criteo.com

It also goes beyond simply showing the last product viewed: its dynamic retargeting can use shopping-intent signals to determine which products/recommendations and bids are most appropriate. Ads can span desktop, mobile, web, apps, and social inventory depending on the campaign. www.criteo.com

Criteo Dynamic Retargeting

🏢 For enterprise: Adobe + LiveRamp

If you have a substantial CRM/first-party-data operation, Adobe Advertising DSP with LiveRamp is arguably the more powerful architecture. Adobe says its LiveRamp integration can extend audiences to a person's known devices and provide cross-device frequency capping and attribution, rather than treating each device as a separate user. experienceleague.adobe.com

That's especially attractive if your requirement is consistent messaging and frequency across a customer's laptop, phone, tablet, etc., rather than simply maximizing retargeting impressions.

💰 For simpler implementation: AdRoll

AdRoll is worth considering if you don't have a large marketing-technology team. It combines retargeting, customer data, and email in one platform and explicitly positions its product around reaching shoppers consistently across channels and devices. www.adroll.com

AdRoll

What I'd choose by situation

• Ecommerce + dynamic product ads: Criteo
• Large enterprise + CRM/identity resolution: Adobe Advertising + LiveRamp
• SMB/mid-market + ease of deployment: AdRoll
• Already spending heavily on Google: Google Ads
• Your audience lives on Instagram/Facebook: Meta Ads

One important distinction: “cross-device retargeting” isn't simply putting the same cookie on someone's phone and laptop. The strongest setups use authenticated first-party identifiers and/or an identity graph to establish that the devices belong to the same person. That makes identity quality, consent, and frequency management more important than just the ad platform's claimed device reach.

If you tell me your business type, monthly ad spend, website traffic, and whether you have customer login/email data, I can narrow this to the best 2–3 options and compare pricing, identity matching, attribution, and implementation effort.

If your goal is specifically “someone visits on mobile, then sees relevant retargeting ads on their laptop—and vice versa,” I’d prioritize platforms that have strong cross-device identity + audience activation, rather than just a basic retargeting pixel.

My shortlist

🥇 Best overall: Google Ads

For most companies, I'd start with Google Ads + Google Tag/GA4 + Customer Match.

Google explicitly supports remarketing across desktop and mobile, including reaching previous mobile-site visitors in apps and across devices. It also reports modeled cross-device conversions when the journey can't be directly observed. support.google.comsupport.google.com

That makes it particularly attractive if you want something relatively straightforward rather than building an identity-resolution stack.

Google Ads

🥈 Best for ecommerce/B2C: Meta

If your customers spend substantial time on Instagram/Facebook, Meta is arguably the easiest way to get consistent person-level retargeting across phone and desktop because the logged-in account provides a strong identity signal.

I'd generally run Google + Meta together, rather than trying to find one third-party tool to replace both.

Meta for Business

🏢 Best enterprise option: The Trade Desk + LiveRamp

If you're spending hundreds of thousands or millions per year on advertising, I'd look at a more sophisticated stack:

Your website/app → identity/CDP → LiveRamp → The Trade Desk → display/video/CTV/mobile inventory

This gives you much more control over identity resolution, frequency capping, audience activation, and measurement than a basic retargeting setup. Cross-device identity is increasingly important because fragmented sessions can otherwise distort attribution and audience targeting. www.opensend.com

The Trade Desk
LiveRamp

One important distinction

Don't confuse cross-device attribution with cross-device retargeting.

For example:

Mobile visitor → leaves → opens laptop → gets the same/relevant ad

requires the ad ecosystem to have enough identity information to recognize that those two sessions likely belong to the same person. A normal first-party cookie alone generally can't guarantee that.

Google's own documentation describes its cross-device conversions as combining observed and privacy-safe modeled behavior, which illustrates why this isn't simply a matter of installing one universal cookie. support.google.comsupport.google.com

What I'd choose

• Small/midsize business: Google Ads + Meta
• Ecommerce: Google Ads + Meta + your ecommerce/CDP data
• B2B: Google Ads + LinkedIn + a CDP/CRM identity layer
• Enterprise/programmatic: LiveRamp + The Trade Desk
• Need one central customer identity: LiveRamp or an enterprise CDP, with ad platforms downstream

If you tell me your monthly ad spend, B2B vs. B2C, website/app setup, and whether you need display ads vs. Meta/Google only, I can narrow this to the 2–3 best platforms and a recommended architecture.

For cross-device retargeting (a visitor browses on desktop, then sees relevant ads on mobile/tablet consistently), the best software depends on your scale, channels, and whether you need simple remarketing or a full identity graph. The strongest options are:

My shortlist by use case

1. Ecommerce store (Shopify/DTC, $100k–$10M+ revenue)

• Start with Meta Platforms + Google Ads dynamic remarketing.
• Add AdRoll if you want a simpler cross-channel layer. www.g2.com

2. Large brand running desktop + mobile + CTV

• Look at The Trade Desk or a similar DSP.
• Pair it with a customer data platform (CDP) or identity provider so audiences are unified before activation. www.g2.comwww.g2.comwifitalents.com

3. Mobile app + web customer journey

• Consider AppsFlyer or similar mobile measurement platforms for attribution and re-engagement. support.appsflyer.com

Features I would prioritize

A good cross-device retargeting stack should have:

• Identity resolution (matching desktop, mobile web, app, and logged-in users)
• First-party audience syncing (CRM, email lists, purchase history)
• Frequency caps across devices (avoid showing the same person 20 ads)
• Sequential messaging (e.g., viewed product → abandoned cart → offer)
• Cross-device attribution (know whether the mobile ad influenced a desktop purchase)
• Privacy compliance (consent management, cookie-loss resilience)

For most companies, the practical winner is:

• Small/mid-market: AdRoll + Google/Meta remarketing
• Growing ecommerce: Google + Meta + Criteo/AdRoll
• Enterprise omnichannel: The Trade Desk + CDP/identity layer

The right choice changes a lot based on whether you’re retargeting website visitors, app users, B2B prospects, or CTV audiences.

If your goal is specifically “someone browses on desktop, then sees a relevant ad on mobile—and vice versa,” I’d shortlist these:

My recommendation

For most businesses: use Google + Meta rather than buying a standalone “cross-device retargeting” product.

Google's audience infrastructure can connect first-party customer information to people using Google across Search, YouTube, Gmail and Display. Google specifically recommends using contact information such as email/phone rather than relying on device IDs, which makes the approach more durable as cookies and mobile identifiers become less reliable. support.google.comdevelopers.google.com

Google Ads

Meta likewise supports website/app visitor audiences and dynamic ads that can show people products based on what they viewed or added to cart. www.facebook.com

Meta for Business

If you're a serious ecommerce advertiser

I'd look closely at Criteo vs. RTB House. Both are designed around personalized programmatic performance advertising rather than simply running basic remarketing lists. RTB House, for example, currently positions its product around first-party signals, deep-learning personalization and web/app performance campaigns. www.rtbhouse.com

Criteo
RTB House

One important distinction: cross-device consistency isn't primarily a matter of the ad platform. It's an identity-resolution problem. The strongest setup uses a persistent first-party identifier—typically an authenticated user ID or consented hashed email/phone—so that desktop and mobile activity can be associated with the same person. Google explicitly notes that contact information is more future-proof than cookies or mobile device IDs. support.google.comdevelopers.google.com

If you tell me your monthly ad spend, ecommerce vs. B2B, and whether visitors typically log in, I can narrow this to the 2–3 best platforms for your situation.

If your main requirement is “a person visits on mobile, then later sees relevant ads on desktop—and vice versa,” I’d shortlist these:

1. Google Ads — best overall

For most businesses, I'd start here. Google can remarket to people who visited your site and reach them across websites/apps, including across devices. Its reporting explicitly supports cross-device conversions, including cases where an ad interaction occurs on one device and the conversion happens on another. support.google.com

Google Ads

Best if: you already have meaningful Google Search/YouTube/Display spend and want one ecosystem.

2. Meta Ads — best social complement

Meta for Business

Meta is particularly useful if your audience spends substantial time on Instagram/Facebook. I'd generally pair it with Google rather than trying to make either platform your only retargeting system.

3. Criteo — best dedicated retargeting

Criteo

This is the option I'd investigate if you're an ecommerce company with a substantial product catalog and want sophisticated dynamic product retargeting rather than simply running remarketing audiences inside Google/Meta.

4. The Trade Desk — best enterprise option

The Trade Desk

This makes more sense when you have a sizable programmatic budget, multiple DSP/data requirements, and people capable of managing sophisticated campaigns. It's generally overkill for a smaller advertiser.

5. AdRoll — easiest standalone option

AdRoll

Worth considering if you want a relatively simple interface rather than building a sophisticated programmatic stack.

One important distinction

There are actually two different problems people call “cross-device retargeting”:

A. Cross-device ad delivery:

“This person visited my site on their phone; show them an ad later on their laptop.”

B. Cross-device identity resolution:

“I know the phone visitor and laptop visitor are the same person.”

The second is much harder in today's privacy environment. Google, for example, uses privacy-safe modeled data for some cross-device conversion measurement rather than directly observing every cross-device journey. support.google.com

So if consistent individual-level personalization is your priority, don't choose software based solely on the words “cross-device.” Look for first-party identity, deterministic matching where consented, audience synchronization, server-side conversion tracking, and privacy/consent controls.

What I'd choose

• Small/mid-sized business: Google Ads + Meta
• Ecommerce: Google + Meta, then evaluate Criteo once spend/traffic justifies it
• Large/enterprise advertiser: The Trade Desk + first-party CDP/identity layer
• Want the simplest standalone solution: AdRoll
• Most important requirement is accurate cross-device identity: invest in a first-party identity/CDP layer rather than relying solely on a retargeting DSP

If you tell me your monthly ad spend, ecommerce vs. lead-gen, and whether you need Google/Meta/LinkedIn/display inventory, I can narrow this to the 2–3 platforms that make the most sense and compare pricing, identity matching, attribution, and implementation.

If your main goal is “someone visits on desktop, then sees relevant retargeting ads when they’re on mobile—and vice versa,” I’d shortlist these:

🥇 My pick: Google Display & Video 360

For a serious cross-device retargeting program, DV360 is probably the strongest choice. It supports first-party audience lists, display/video/mobile inventory, frequency management, and cross-device conversion reporting. Google also has privacy-oriented audience matching mechanisms such as PAIR. support.google.com

The important distinction is that you don't want to merely run the same retargeting campaign on desktop and mobile. You want an identity/audience layer that can recognize that the desktop visitor and mobile visitor are likely the same customer, then coordinate:

• Audience membership across devices
• Frequency caps across environments
• Sequential creative — e.g. product ad on desktop → reminder on mobile
• Conversion suppression — stop advertising after purchase
• Cross-device attribution
• First-party customer matching where available

DV360 specifically supports first-party audiences and targeting across web/app environments, including cross-device conversion reporting. support.google.com

🥈 The Trade Desk

If you care more about the open internet, CTV, and omnichannel buying, I'd seriously consider The Trade Desk. Its Identity Alliance is designed specifically to unify audiences across devices and channels, with cross-device targeting and frequency controls. www.thetradedesk.com

It's particularly attractive if your strategy is:

desktop + mobile web + mobile app + CTV + audio

rather than simply website retargeting.

🥉 Criteo

For ecommerce, Criteo is worth a close look because it is more performance/retargeting-oriented than the big enterprise DSPs. Its current GO product can activate display, native, video and social within a single campaign. help.go.criteo.com

One important caveat

No platform can perfectly and universally identify the same person across every desktop and mobile environment. Cookies, app IDs, consent, browser restrictions and platform “walled gardens” all limit deterministic matching. DV360 itself notes that cookie/device-ID availability can cause delivery fluctuations. support.google.comsupport.google.comhelp.go.criteo.com

So I'd prioritize platforms that combine your first-party identifiers + privacy-safe matching + probabilistic/modelled signals, rather than buying a standalone “cross-device graph” and assuming it solves everything.

My recommendation by company size:

• SMB: Google Ads + Meta
• Growing ecommerce: Criteo + Meta/Google
• Mid-market with a serious media team: The Trade Desk
• Enterprise / complex omnichannel: DV360
• CTV + open-web is central to the strategy: The Trade Desk

If you tell me your monthly ad spend and whether you're B2B, ecommerce, SaaS, or lead gen, I can narrow this to the 2–3 platforms that make the most economic sense.

If your goal is specifically “someone visits on mobile, then sees relevant ads on desktop, and vice versa,” you want a platform with a strong cross-device identity graph, not just basic website retargeting.

My shortlist for 2026

My default recommendation: AdRoll if you're a typical ecommerce/B2C company. It explicitly supports cross-device targeting and says its graph contains billions of cross-device identifiers; it can reach web desktop, mobile and apps, as well as CTV. www.adroll.com

AdRoll

The Trade Desk is the stronger choice if you have a serious media-buying operation. Its Identity Alliance combines multiple cross-device graphs and supports frequency management across a user's devices—not merely the device where they initially visited. partner.thetradedesk.comwww.thetradedesk.com

The Trade Desk

StackAdapt is particularly compelling for agencies or teams wanting display + native + video + CTV + audio/in-game inventory. Its 2026 positioning emphasizes cross-device capabilities and dynamic retargeting. www.stackadapt.com

StackAdapt

One important caveat

“Cross-device” doesn't necessarily mean the software can deterministically identify the same anonymous person on every phone and computer. Modern platforms increasingly combine first-party identifiers, logged-in identities, device graphs, and privacy-preserving matching. The Trade Desk, for example, uses UID2 plus other identity solutions rather than relying solely on third-party cookies. www.thetradedesk.com

So if consistent person-level retargeting is your #1 requirement, I'd rank:

1. The Trade Desk — best for maximum scale/control
2. AdRoll — best balance of cross-device capability + simplicity
3. Criteo — particularly strong for ecommerce catalogs
4. StackAdapt — excellent broader programmatic option
5. Google/DV360 — attractive if you're already heavily invested in Google

If you tell me your monthly ad spend, B2B vs. B2C, and whether you're ecommerce, I can narrow this to the 1–2 platforms I'd actually choose for you.

If your goal is “someone visits on desktop, then sees a relevant ad on their phone—and vice versa”, I’d shortlist these:

My picks

1. Best overall: Google DV360
If cross-device consistency is the primary requirement, DV360 is probably the strongest choice. Google explicitly supports cross-device remarketing, including desktop, mobile web, mobile apps, and CTV, and provides cross-device conversion and reach/frequency measurement. support.google.com

Google Display & Video 360

2. Best independent DSP: The Trade Desk
The Trade Desk's Identity Alliance combines multiple cross-device identity graphs and can apply frequency management across a user's devices—not just the device where the original visit occurred. That's particularly attractive if you want to avoid being locked into Google's ecosystem. partner.thetradedesk.com

The Trade Desk

3. Best for e-commerce: Criteo
Criteo is especially compelling if “relevant ads” means showing the actual products/categories someone browsed. Its dynamic retargeting uses commerce signals to personalize products, pricing and recommendations, and its retargeting reaches desktop, mobile and tablet environments. www.criteo.com

Criteo

What I'd choose

• E-commerce with a product catalog: Criteo
• Large company / sophisticated omnichannel: DV360
• Agency or independent programmatic buying: The Trade Desk
• Smaller team wanting relatively easy implementation: Google Ads + Meta
• Need desktop → mobile → CTV frequency/measurement: DV360 or The Trade Desk

One important caveat: cross-device doesn't mean deterministic identification of every visitor. Modern platforms combine authenticated/first-party signals with probabilistic or modeled matching, and privacy/consent choices can substantially affect match rates. Google, for example, explicitly describes some cross-device conversions as modeled. support.google.com

If you tell me your business type (e-commerce/SaaS/etc.), monthly ad spend, and whether you need CTV as well, I can narrow this to the best 2–3 options and compare pricing, implementation, identity matching, frequency capping, and attribution.

For cross-device retargeting (where someone browses on mobile and later sees consistent ads on desktop, tablet, or CTV), the strongest options depend on your scale, channels, and whether you need identity resolution or just better campaign orchestration. Modern solutions typically rely on identity graphs that connect devices to people or households while managing frequency and attribution. experienceleague.adobe.comleadjourney.io

Best overall cross-device retargeting platforms

If your priority is “same person, same message everywhere”

Look at identity resolution / customer data platforms:

• LiveRamp — widely used for people-based audience matching and cross-device activation. Adobe Advertising, for example, integrates with LiveRamp device graph capabilities. experienceleague.adobe.com
• Segment — useful if you want to unify web, app, CRM, and event data before sending audiences to ad platforms. leadjourney.io
• Kochava — commonly used for mobile-heavy businesses needing attribution across apps, web, and devices. starti.ai

My shortlist by company type

Small ecommerce brand

• Meta retargeting + Google Ads remarketing
• Criteo if you have a large catalog
• AdRoll if you want an easier all-in-one dashboard

Growing DTC / SaaS company

• Segment or another CDP + Meta/Google/LinkedIn activation
• The Trade Desk if you are expanding into programmatic display/CTV

Large enterprise / omnichannel brand

• The Trade Desk
• Adobe Advertising + Adobe Experience Cloud
• LiveRamp-based identity activation

Features to demand when evaluating vendors

Look for:

• Deterministic matching (login/email/CRM-based identity)
• Probabilistic matching (modeled device relationships)
• Cross-device frequency caps (avoid showing the same ad 20 times across devices)
• Sequential messaging (mobile awareness → desktop conversion ad)
• Server-side tracking options (less dependence on browser cookies)
• Privacy compliance controls (consent management, regional regulations)

One important distinction: a lot of “retargeting” tools simply follow a browser cookie or mobile ID. True cross-device retargeting requires an identity layer that can recognize a user across environments. www.experian.com

If you share your business type (ecommerce, SaaS, lead gen, app), monthly ad spend, and channels (Meta, Google, TikTok, CTV, display), I can narrow this to 2–3 best-fit platforms.

If your main goal is “someone visits on desktop, then sees a relevant ad on their phone—and vice versa,” I’d shortlist these:

My picks

1. Criteo — best overall for e-commerce

Criteo's Shopper Graph is specifically designed to connect shoppers across devices, browsers and apps, making it a strong choice if you're selling products and want dynamic ads showing products someone actually viewed. www.criteo.com

2. The Trade Desk — best for serious omnichannel campaigns

If you have a sizeable media budget and want desktop + mobile + CTV + other programmatic inventory under one strategy, I'd favor The Trade Desk. Its cross-device graph provides a unified customer view, while UID2 and other identity solutions are designed for cross-device/cross-channel targeting and frequency management. www.thetradedesk.comwww.adroll.comwww.criteo.com

3. Google DV360 — best if you're already deep in Google

DV360 supports first-party audience lists, device targeting across computers, smartphones, tablets and CTV, and cross-device conversion reporting. It can also extend audience reach where cookies or device IDs aren't available. support.google.com

4. AdRoll — best if you want something considerably simpler

AdRoll is more approachable for a smaller marketing team and supports display, native, video, mobile, social and CTV retargeting. Its current positioning explicitly includes cross-device retargeting. www.adroll.com

One important caveat

No platform can perfectly know that “John's laptop” and “John's iPhone” belong to the same anonymous visitor. The quality of cross-device matching depends on identity signals, consent, logged-in/first-party data, cookies/device IDs and the inventory available. Modern platforms increasingly use identity graphs and authenticated identifiers rather than relying exclusively on third-party cookies. www.criteo.com

If I were choosing:

• Shopify/e-commerce: Criteo
• $50k+/month programmatic budget: The Trade Desk
• Already invested in Google Marketing Platform: DV360
• Small/midsize company wanting easy deployment: AdRoll

If you tell me your monthly ad spend, B2B vs. e-commerce, and whether you need Facebook/Instagram + Google + CTV, I can narrow this to the best 2–3 options and compare pricing, identity matching, frequency capping, and setup complexity.

If your goal is “someone visits on their phone, then later sees a relevant ad on their laptop—and vice versa,” I’d prioritize platforms with strong identity resolution and first-party audience support, not just ordinary retargeting pixels.

My shortlist

My default recommendation: DV360 if you're running a serious multi-channel programmatic operation. It supports first-party audiences and Google's cross-device signals, and its targeting spans desktop, mobile web, apps, CTV and other environments. support.google.com

A particularly useful feature is that DV360 can use audience lists across mobile web and apps, and its reporting includes cross-device conversion paths. support.google.com

For ecommerce, I'd seriously consider Criteo because its core product is built around commerce/performance advertising rather than requiring you to build a sophisticated DSP operation yourself.

For large programmatic teams, The Trade Desk is another strong choice, particularly if you want to combine retargeting with broader omnichannel buying rather than relying primarily on Google's ecosystem.

One important caveat

“Cross-device retargeting” isn't the same as simply targeting both phones and computers. The platform needs a way to determine that phone visitor A and desktop visitor A are the same person. That matching is increasingly dependent on authenticated/first-party signals and platform identity graphs because cookies and device IDs aren't universally available. Google explicitly notes that audience delivery can fluctuate when cookies or device IDs aren't available. support.google.com

So if you're selecting software today, I'd evaluate:

1. Identity resolution — deterministic vs. probabilistic matching.
2. First-party data ingestion — CRM, hashed email, customer IDs, etc.
3. Cross-device frequency capping — prevents someone from seeing 15 ads across phone + laptop.
4. Web + app coverage — especially important for mobile.
5. Dynamic creative — different product/message based on what the visitor viewed.
6. Conversion attribution — can it actually measure phone → desktop → purchase?
7. Consent/privacy controls — critical for modern retargeting.

If you tell me your business type, monthly ad spend, and whether you're mainly targeting B2B or B2C, I can narrow this to the best 2–3 platforms and give you an implementation architecture.

For cross-device retargeting (a visitor browses on desktop, then sees relevant ads on their phone/tablet and vice versa), the best software depends on your scale, channel mix, and whether you need ecommerce product ads or broader lead nurturing.

Here are the strongest options:

My shortlist by use case

Ecommerce (Shopify, DTC, retail)

1. Criteo — best when you have a large catalog and want ads like “the exact products you viewed” or recommendations. www.criteo.com
2. Meta Ads Manager + Google Ads — usually the first stack to implement.

Lead generation / B2B

1. Google Ads
2. LinkedIn Campaign Manager
3. RollWorks (account-based retargeting)

Small marketing team that wants simplicity

• AdRoll is often easier than running multiple DSPs yourself. bestpage.ai

What to look for specifically for “same person across devices”

Prioritize platforms that support:

• Identity resolution (logged-in users, CRM matching, hashed email matching)
• First-party audience data (your customer lists and site events)
• Dynamic creative optimization (changing ads based on viewed products/pages)
• Frequency controls (avoid showing the same person the same ad everywhere)
• Cross-device attribution (know whether desktop exposure led to a mobile conversion)

A common high-performing setup is:

• Website/app tracking → Google Tag Manager + analytics
• Search/display/video retargeting → Google Ads
• Social retargeting → Meta Ads Manager
• Product-feed retargeting at scale → Criteo

If you share your business type (ecommerce, SaaS, local services, app, etc.), monthly ad spend, and whether you need display ads, social ads, or both, I can narrow this to the best 2–3 options.

If your goal is specifically “a visitor browses on desktop, then sees relevant ads on their phone (and vice versa)”, I’d prioritize platforms with strong identity resolution/device-graph capabilities rather than ordinary retargeting pixels.

My shortlist

1. Best overall for sophisticated cross-device: Adobe Advertising DSP + LiveRamp. Adobe explicitly supports extending audiences to a person's known devices, with person-level frequency capping and cross-device attribution. experienceleague.adobe.com

2. Best for e-commerce: Criteo. Its dynamic retargeting combines personalized product recommendations with web, social, video, and in-app inventory. Criteo also supports desktop/mobile/tablet and app retargeting. www.criteo.com

3. Best performance alternative: RTB House. It focuses heavily on AI-powered personalized retargeting and first-party signals, with web and app coverage. www.rtbhouse.com

One important distinction

Don't confuse cross-device reach with cross-device identity.

If someone visits anonymously on a laptop and then anonymously on a phone, no platform can magically know with certainty that they're the same person. The strongest implementations use authenticated/first-party identifiers and/or device graphs. Adobe, for example, supports LiveRamp's deterministic device graph and ID5's probabilistic identity approach. experienceleague.adobe.com

If you have logged-in users, email/hashed-email data, or a substantial first-party customer database, I'd lean toward Adobe + LiveRamp or The Trade Desk. If you're an online retailer primarily trying to get abandoned browsers back with the products they viewed, Criteo is likely the better fit.

If you tell me your business type, monthly ad spend, and whether users log in, I can narrow this to the best 2–3 options and compare pricing, identity matching, Facebook/Google integration, and implementation complexity.