Photoshop, imo its more advanced though things you can do in Photoshop you can also create in gimp (userbars) for example can be made with both programs and its easy as well.
I don't dislike Photoshop, but GIMP is great because it's easy to use and free. I used to have Photoshop, but I lost it due to formatting my hard drive.
I've only used a bare bones(default everything) Photoshop in class a few times, and it's just too much hassle for me. In Gimp I know where pretty much everything is and I know how to make it do what I want.