Over the years I have tried many, the older JR (don't recall the number), the Airtronics 94145, the Futaba 9602 and most recently the KO 949. I have to say each and every one of them worked well and the KO is still bolted in to my Rev.4 and working perfectly.

I would say that if you went with a quality unit along the lines of what everyone has mentioned here you will be in good shape. In 12th scale the servo is never something that you should buy used or skimp on, having a car that won't center up can be hell.

Nick