I'm going to have to say N64. Wave Race 64... come on... one of the best racing games ever. Mario Kart, F-Zero, Beetle Adventure Racing. It did lack some of the more serious racing games. Maybe it's due to size constraints of cartridges.
The Playstation would be the choice for simulation fans. Gran Turismo has the ability to trump them all. But aside from that, I don't think it had much going for it. Ridge Racer seems to be the claim to fame. But I've never been a fan. I prefer simulation style racing games, but not from that era. The system was just too weak.
Sega Saturn has them beat on arcade racers. Outrun, Daytona USA, Hang on...
Interestingly enough, each system had it's own flavor of racer. Nintendo specialized in fun Kart style racers, Sony with simulation, and Sega for arcade. It depends on what style you like most. I seem to have more fun with Nintendo racers though. Plus 20% of the library seems to be racers. So, there are bound to be some good ones.