I have been using both. made small things just to experiment. My opinion is that (at least on first look) UE seems more powerful than Unity. though that's a first impression. By default UE graphics seems better than Unity, same goes for physics engine. (Keep in mind that UE has blueprints too that makes it easier to handle some things). In the end though try to make something small on both engines and then choose. I think in order to choose you have to think what you want to make.