Every engine I've used has some really good stuff and some surprising limitations.
For Frostbite... If you've worked with it you know. Probably my least favourite.
In UE4 I love the environment but can't get over how cumbersome some aspects of graphics programming are. Especially how difficult it is to work with compute shaders.
For Unity I really like how smooth the workflow is, especially for shader programming. Having used it for a little more than a year now I'm really surprised how nice it is to work with. I barely even mind it being primarily C#.