I'm largely cheating here, because slow car fast is always the most fun.
Except slow car that's not quite slow fast.
Mazdaspeed Miata. It's the only car I've ever owned that I'd buy the exact same car again.
Wiggles
Which car did you own that was the most fun to drive. I think for me it was my 1997 Subaru Outback Legacy. It wasn't super powerful, there was a lag when you hit the gas, but there was just something so intimate about the way it handled, especially on curvy country roads.