Z-cars. So much diversity, a TON of history, and no one judges. Awesome long-running conventions all over the country, tons of local clubs (official and unofficial), and the cars are rare enough for them to be kept alive and restored, but not so rare that people are afraid to drive them as they were intended.

Second place to track rats like someone mentioned below. At a track day, even the novices (like myself) are treated as equals by guys with 100x the experience and 100x the car.