There are many different types that you could use.
I have photoshop CS3...*cough* that i found on the web *cough* <_< ...and play with it alot (too comfusing to do too much with it). To toss another program at you there is Corel which a friend uses and loves. I heard is was good for more background stuff and more color variety.
But between Photoshop and Illustrator I cant help much... I would say to go to deviantART.com and look for some art done by both types and talk/PM to the artists there. Most likely there is a forum of artists debating the same thing somewhere on the site.
