I played Super Mario World and Super Mario Allstars my entire childhood, it was what got me into gaming. But the 3D-Mario games are one of the greatest gaming experiences I have.
But 2-D by a veeery small margin.
Predictions for December 31st 2008:
Wii 38,000,000
DS 84,500,000
PS3 17,000,000
PSP 41,000,000
X360 23,000,000