What is the most accurate ecommerce attribution method in 2025?

There isn't one. If you're looking for a single named model that nails it every time, you won't find it, and anyone selling you that answer is selling something else too.

The closest you'll get in 2025 is a hybrid: incrementality testing (holdout groups, geo-lift tests) layered on top of a unified data model that blends marketing mix modeling (MMM) with multi-touch attribution (MTA). None of these on their own is reliable anymore. iOS 14.5+'s App Tracking Transparency, Chrome's slow cookie phase-out, and the growing gaps in server-side tracking have all chipped away at single-touch models like first-click or last-click. They were never perfectly accurate, but they used to be close enough. Not anymore.