Of course it depends on application, but in my personal experience I've been very happy with the MKS and Savox servos. I have the MKS 550 in my MP10 for both steering and throttle/brake and they have plenty of speed and torque for the buggy. In my 1/10th scale I run the Savox servos. They're fast and affordable and I have had no problems with either.
Whatever you go with just be sure to get something with enough speed and torque for what you need. A poor or slow servo can really make for a disappointing experience with your car.