Mmmmm... well, to answer the dumb question...

Rear wheel drive, very high power-to-weight (10hp:lb min), very light weight (under 1000 lbs), lots of aerodynamic downforce, very wide sticky tires (10-12" wide), well-engineered suspension, several thousand dollars worth of shocks... yeah. That's a start.

For those in the know, I'm describing a competitive A-Mod car, of course. That would be the ultimate and best autocross car. (and most people aren't capable of thinking fast enough to drive it to its fullest!) Somehow, I don't think that's what our misguided newb was asking.

Now, lest we scare him away by being a bunch of dicks... Hondahunter, you need to ask a more specific question. Best autocross car... for what class? (do some research) For what budget? And... what do YOU like to drive? Will this be an autocross-only car, or also a daily driver? Trailered or driven to events?

Your best bet is to get out to an autocross in WHATEVER car you own and start getting a feel for the sport. It really doesn't matter much what you drive until you get yourself a good ways up the learning curve as a driver.