The best car I've ever had a ride in was this black 1994 McLaren when I was about...9 or 10.
The car belonged to a friend of one of my relatives who was a self-made millionaire in Monaco. Anyways, during a family event, I had caught the car outside on the street right in front of a little "Tourist Souvenir" shop (a shop I would work for in 8 years). As I gawked, the man (won't reveal his name; I've just managed to contact him lately) asked me if I would like to sit in it.
I remember seeing those butterfly doors just open up, like a rocket ship, and just climbing into the passenger seat. Then he asked me if I wanted to go for a ride. I replied the obvious as my great-grandpa smiled.
He started it up, and damn, it was amazing. Everyone on the street just flocked to it. I felt like a star, or something. The drive was about 5 minutes, but it was the best 5 minutes of my life, esp. listening to it hit those high RPMs under the Fairmont Hotel. Well, years down the road, I learned he had moved to New Zealand for a short time, and now resides back in the hills of Monaco.
As for the best car I've driven, I'd probably say the Murcielago Roadster or Diablo VT. The Diablo VT, though, is definately more of a power-monster, and requires a gentle foot to keep it from going wild.