Diddy who?
No, clearly F-Zero. DK Racing was nice back in the N64 days. But that was mainly because of the single player. Multiplayer never was as good as Mario Karts.
And Wii U already got two good fun racers with Mario Kart (espacially MP) and Sonic Transformed.
F-Zero is something we haven't got in a very long time and something, no other console has of now. And today it could have great single player as well as online mp.