Cheap Miata gets my vote. I had a '96 and the purity of the driving experience cannot be explained. It makes my E46 BMW feel ordinary in comparison. Not the fastest in a straight line but when the line curves the Miata doesn't need to slow down
They're cheap to buy, cheap to insure, and cheap and easy to maintain. AFAIK you can still get discounted go-fast parts through MazdaComp if you auto-x it a few times per year. If you want to go fast in a straight line turbo is always an option, either home brew of one of several very well sorted kits that'll net you reliable, daily-driverable 250+ wheel horsepower.
Scott
