I did't list "Paint Shop" in the list of products GIMP is more powerful than, because frankly, I think GIMP is only competitive with Paint Shop 9. But I don't retract the claim of "best," because for 100% less money and for continually free updates, I still think GIMP is the best out there.
Frankly, my Corel products (which do NOT include Paint Shop) crash or lock up all the time, and while I have enjoyed my opportunities to play with Paint Shop, I think that's a pretty huge detraction. Unlike OpenOffice, I have used GIMP for quite a while. I never had trouble with it. (Except for when I switched OSs, it crashed because I needed an update of GTK+.)
Some people don't like the multiple windows GIMP uses. After taking some time getting used to it, I prefer it; it allows for sharing space better on my desktop. I very much like the interface on GIMP, but I know many hate it. That's a mattter of preference.
Now, Corel is pushing heavily Paint Shop X. I think it has some very cool new features, and may has just outpaced GIMP as far as power.