Diddy kong racing was my most enjoyable racer because of the adventure elements in it. But we're not comparing that sooo. I'll go with mario kart64 even though I had a blast playing the CTR demo with friends.
Didn't CTR come out a couple years after MK64? N64 had some good ass 3D graphics that PS could never achive.
Off tpoic: I'll take PS over N64 because of the awsome 2D games and rendering power it had. But some of those 3D games N64 had still blow me away every time I see them.