The higher the torque, the better.

With high torque servos, you can use a long servo arm and end up with ridiculous speeds.

My personal favorite steering servo is the Towerpro MG 959, 190oz or torque at 6 volts, is coreless, digital, metal gear, BB, has a nifty aluminum case, and runs about $30.

As for throttle, I like my futuba 3050. The 3150 is also a fantastic, affordable servo.