I agree with raizenpk, that's what the 30 day trials are for. But also understand why the question of which is 'the best' is being asked in the first place. Is there anything as good as Adobe's products? If not, then why hasn't anyone tried to complete with them? Adobe just seems to be the industry standard and they charge for their products like they know that...college licensing is just as expensive and complicated to upgrade.
I think 90% of people could easily get by with Photoshop Elements. The spot healing brush in CS2 (Space Monkey) was a nice addition back in 2005. Since then, I haven't really found much use for (m)any of the new features. At least not on a daily basis. New doesn't mean better. Anyone who buys something simply because it's newer is a moron and a slave.
I'm about to buyt Photoshop CS5. The last, the best so far. I heard it includes some new features and it basically does some of the job all by itself.
theres a pretty good free watered down online photo editor online called http://pixlr.com It operated on layers and can open psd's. It works for someone like me who hates graphic design but occasionally needs to do some thing.