Had to go with GX although it was a close one with F-Zero X.
X had the speed down and I loved the Death Match mode which was basically just crash into as many drone cars as possible.
GX is very much like X but with better graphics, a merciless story mode and more frizzles. Honestly I think even with the lame background images I liked some of X's tracks more but all in all I have to give it up GX.
Seriously, I don't get why Nintendo hasn't at least tried to make a new game on the 3DS at least, Captain Falcon is popular enough in Smash... USE IT and not just water it down with a lame generic racing anime or more attempts to improve on the SNES version like with all those GBA sequels.