They're all great cars. I don't think you'd be able to go wrong whichever you chose, as you long as you can find parts for the car you select where you'll be racing. I know parts availability isn't the issue it once was, but I try to get all my parts and supplies at the track where I race. It's my way of helping keep the place going, and I don't mind spending a little extra over mail order prices. You can't race by mail if the track goes out of business...

The 9650 is a great servo, and any 1/12 car that comes with holes already drilled for a servo will be an exact fit. I run the JRz3650, but as far as I know the CRC GenX is the only car of the ones you've mentioned that has holes predrilled for the JR as well as the Futaba (Airtronics and KO 1/12 scale servos fit the same pattern as the 9650) The BMI >might<, but I don't know for sure.