It's just been revealed that it will be coming to the Wii U, so that has an appeal, but I got the first one for the Xbox 360 thanks to the extra
characters of Banjo & Kazooie (no one else had any
guests), the ability to use your Avatar (or Mii on the Wii, and no unlocking yourself here as in Mario Kart),
downloadable content (Metal Sonic and a Death Egg track), plus Achievements.