Depends on what I want to do.
If it's pixel art, I go for:
1) Brilliance/True Brilliance
2) DPaint
3) PPaint
If it's scanned/photo art:
1) Photogenics
2) PPaint
3) ImageFX (This is actually a very good package, it is just that I'm more familiar with others, so I reach for them first... If I had more experience with IFX, it would probably be my first choice for this.)
And, of course, if it needs to be scaled, changed format, whatever:
1) AD Pro :-)