bw7 makes a good pitch for the gba, and really it shouldn't be ignored. but i can relate with the need to play a home console.
really, beyond that, you're not all that picky. essentially, you can't go wrong with any of the three. they all have their pros and cons. they're all relatively similar in price and technological abilities.
at this point, it simply depends on which games most catch your eye and interest. so, here's a list of the more appealing games for each system. granted, some games appear (or will appear) on more than one of the consoles, but those listed are most closely associated with the console its listed under, and typically perform the best there.
gamecube:- metroid prime
- the legend of zelda: wind waker
- super smash brothers
- resident evil 4
- eternal darkness
- pikmin
- soul calibur II
ps2:- GTA
- metal gear
- jak and daxter
- ratchet and clank
- final fantasy
- red faction
- castlevania
xbox:- halo
- splinter cell
- ninja gaiden
- star wars: knights of the old republic
- dead or alive
- mech assault
- fables
