GODOT, easy, 100% free. tell users what do you want from a game engine. it's actually really nice and easy to me. when i see unity, i scare a lot! but Godot... it's nice to me. a least. and if you think it don't have something that you need, get some plugins, or if you are very good at programming you can get sources and change what do you want, or add, or remove (i actually don't know how much you are free to change source code and use it, you should see here).