Diddy Kong Racing.
Mario Kart 64 was the weakest in the series.
DDR had great novetly by adding missions to a kart racer.
MK64's damnable cheating AI. Seriously, no matter how much of a lead you gain, the CPU will always be right on your ass. Really. Just change your map option to the grid option and watch as the 2nd place and 3rd place CPUs gain the same speed boost to keep up with you no matter how fast that Star and Gold Mushroom is accelerating you.
DKR's tracks and music were just so much better.
MK64's Rainbow Road? SNNNNNnnnnnnnnooooorrrrreee...
Very clever power-up system, with upgradable weapons that were never overpowered or gamebreaking. I'm talking bout DDR here.
DDR's boss races.
Diddy Kong Racing.