I disagree, the UI and hotkeys on GIMP are terrible, PS is much better for all levels. Except that it is paid.
But really so long as you get used to it then it doesn't matter.
Somethings made in SAI by me so you can see the sort of things you may be able to do, A lot of images.
Yes corel is great. But it depends on what u want to do.
I personally use photoshop, it's easyer to work with layers.
I personally never understood gimp, idk to use it...
And another program i heard of is Mudbox. If u want to create a full jt set that helps. I've heard u can draw directly on the sphere there...draw on a 3d object.
Or even beter, if torrents are allowed in your contry try to use all 4 ;) mix them, they all have specific advantages and disadvantages...