Get Mario Kart because they're always (usually)solid games, and you know it'll be fun, and it's allot cheaper than buying a DS for The World Ends with you when it may not be a good game.
You rich !@#$%. I wish I could afford AIDs.
I would strongly reccomend the DS path, as FF3,Advance Wars, Phantom Hourglass,Sonic Rush and loads more good games are out/coming out on it, whereas Mario Kart wii is just one good game.If you get the chance though, get both.