Play Framework: Built on top of Akka, non-blocking architecture (offload any long-running work into Futures), mature codebase and APIs for Java and Scala. It's an opinionated framework where you'll write your code in a classical MVC style (define endpoints in a routes file which are then handled by controllers).

http4s: Focused on functional programming, more of a library than a framework. Doesn't define the architecture of your program as much as Play and can therefore be integrated into your project more easily if you want to add HTTP to an existing project.

I enjoy working with either of these two. Pick Play if you want a framework (contains everything to get going with HTTP but forces a certain architecture). Pick http4s if you want a library and/or more focus on functional programming.