I've shipped Unity games, and had impact on some engine decisions for major companies (between Unity, Unreal, and a few others).

Unreal is a FPS engine with a gorgeous renderer. Unity is a rendering pipeline, physics engine, with a C# interface.

Are you making a movie? Unreal. Making a FPS (or third-person, I guess. an ego shooter? whatever.) Unreal.

Making literally anything else: Unity. It's that simple.