I've used Photshop 5- CS2 and Paint Shop Pro 5-10 also GIMP. If you're running a Mac or a PC and have 200$ or more dollars to spend buy Photoshop CS 2! It's incredibly powerful and used by proffesionals in every area. Older versions of Photoshop range in price from 100-200$. Still incredible. Paint Shop Pro, I never found my liking for this program. Not as much as support or tutorials/resoursces for it on the web. It's really not as powerful and I wouldn't recomend buying it. GIMP on the other hand is free yet a bit hard to use. Enjoy ^^
I don't know what program is the best since I'm not so a professional graphic designer, suck even hehe. I like PhotoImpact. It's easy for beginners and has a lot of build-in graphic material.