Your business has a website and an app, and you want to analyze user journeys across these two platforms, as well as see how new users arrive at your website and app. Which of the following should you use for these insights?

You should use Google Analytics properties. A single property can collect from a website and from iOS and Android apps through separate data streams, and because all of it is recorded with the same event-based data model, journeys can be analysed across platforms instead of in separate silos. That covers both halves of the question: acquisition reporting shows how new users first arrive on each platform, and cross-platform analysis shows what they do afterwards, including journeys that begin on the web and finish in the app. Adding User-ID strengthens this further by joining a signed-in person's activity across devices. Firebase remains relevant for app development and diagnostics, and Google Marketing Platform covers advertising and measurement products, but the unified journey analysis described here happens in an Analytics property.