If you are short on money, I would recommend buying one at a time and possibly trying out (or at least reading reviews) games before you buy them to see if you like them.
To find reviews go to
www.metacritic.com Find a game and Metacritic will display a big list of links to reviews of that game from all the major publications.
EDIT: If you love fighting games the GCN has good ones like Mortal Kombat Deception and Soulcalibur 2, and Super Smash Bros. which is non-traditional but probably better than them all. However for traditional fighting games PS2 is definately the best with exclusives like Virtua Fighter 4 and Tekken 5.
However overall you can't go wrong with either system, there are tons of good games for both.