If you want an xbox get an xbox. If you want a wii then get a wii. If you want a ps3 then get a ps3. If you want a pony made of brass, get a pony made of brass.
Why ask these opinion based question?
Are you incapable of making descisions?
You are the one who will be paying/playing it.
As far as online games for xbox. Gears of War is the current fad. It will die out in a couple of months. Halo 3 will come out, and rinse and repeat.