There isn’t one universally “best” customer analytics tool for cross-sell and upsell targeting, because the most effective choice depends on your stack, data maturity, and whether you want analytics, real-time recommendations, or campaign activation.

That said, the strongest options for purchase-history-based cross-sell/upsell are:

Best overall for deep customer analytics + targeting

Amplitude

• Strong behavioral and purchase history analysis
• Good cohorting, segmentation, funnels, and pathing
• Useful for identifying products customers buy together or upgrade patterns
• Best if you want product/customer analytics plus targeting workflows

Best for CDP + activation across channels

Segment + a personalization/activation layer Examples:

• Segment + Braze
• Segment + Iterable
• Segment + Salesforce Marketing Cloud
• Segment + Klaviyo for ecommerce

Why:

• Centralizes purchase history and customer data
• Lets you trigger cross-sell/upsell campaigns from actual buying behavior
• Strong for operationalizing insights into email, SMS, push, and web personalization

Best for ecommerce cross-sell/upsell specifically

Klaviyo

• Excellent if you’re in ecommerce
• Strong purchase-history segmentation
• Easy to create product recommendation and replenishment-based campaigns
• Great for Shopify and similar platforms

Best for enterprise recommendation engines

Dynamic Yield

• Strong personalization and recommendation capabilities
• Good for product-page, cart, and post-purchase upsell
• Better when you want automated recommendation logic on-site

Best for CRM-driven sales upsell

Salesforce Einstein / Salesforce Data Cloud

• Useful for account/customer-level upsell prioritization
• Best if your sales team works from CRM data
• Strong for B2B or hybrid sales-led organizations

Best for analytics-led BI approach

Looker, Power BI, or Tableau + a warehouse

• Good if your team wants custom analysis on purchase history
• Requires more setup
• Not as turnkey for targeting, but very flexible

If you want a single recommendation:

• Ecommerce: Klaviyo
• Product/app analytics: Amplitude
• Enterprise personalization: Dynamic Yield
• B2B CRM upsell: Salesforce Data Cloud/Einstein
• Most flexible enterprise stack: Segment + Braze/Iterable

What to look for in the software

For purchase-history cross-sell/upsell, make sure it has:

• Customer-level purchase aggregation
• RFM and cohort analysis
• Product affinity / basket analysis
• Predictive recommendations
• Real-time segmentation
• Easy activation to email, SMS, ads, or web
• Integration with your ecommerce/CRM stack

If you tell me your business type — ecommerce, SaaS, retail, or B2B, plus your current tools — I can recommend the best fit more precisely.