Neither personally. MK Wii was such a disapointment for my friends and I. We all find MKDD to be the best console MK. If you don't necesarily have friends to play with locally, I'm sure either MK will fill your needs with online play. Just the Wii version will allow for people to play locally when you want, so that right there would win me over.
Heres hopnig to a better Maro Kart in the future!