Unity Engine has become super duper popular here recently. If you're wanting to create mobile games or any sort of platformer then it's definitely the way to go. It's good for full on 3D games as well. Personally though, I still a really big fan of Unreal Engine. The blueprinting system is great and I feel like the graphics are still superior to Unity. If you're developing a 3D game (like Witcher or Shadow of Mordor) then high quality graphics is definitely a top priority. That was one of the main reasons I switched from Unity to Unreal. So I guess it depends a lot of what kind of game you want to create.