I'd say Paint Shop Pro, since I have GIMP and I don't think it's anything great- just a very weak version of Photoshop.
If you're just starting out, get Gimp -- It's free, and you can see if you like GFX before you spend money on expensive programs.
I wouldn't recommend buying a program you don't know how to use. Try GIMP out first, and once you get the hang out it, then you could buy Photoshop if you wanted to.