Of course it depends, if you like rpgs, i'd get a gameboy sp and as the final fantasy's. the flaw for gba is...well, its a game boy, it has its limits. or get a ps2 for more rpg with the final fantasy series, and more games than you can shake a stick at, plus some great quality games such as gta, need for speed and medal of honor, too bad you need a multitab for 3-4 players. X-box is for more less a more mature players, with real good games like of course hale 1 & 2, kotor 1 & 2, fable and some other games i cant remember, but to play online cost cash...
Then finnaly is the gamecube. its got great series such as zelda and mario, has high quality mature games like resident evil 4. And you have more e rating games, like monkey ball (lol) and animal crossing. Then we have lots of great upcoming games such as fire emblem, advance wars, legend of zelda and star fox. The cube mostly speciallises in multiplayer without online, + i find they have the best controller of the 3 conslles

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Overall, you pick on what you like, i have the cube, ps2 and a gameboy sp.