I personally would say a good digital ti gear high torque servo. High speed servos are lower torque so it may have the speed but if if can turn the wheels and hold it; it just is not going to work for you. A 333oz Hitec is plenty fast enough.
For a buggy I'd want speed. Savox makes some fast and high torque servos for reasonable prices. You can go with a high voltage servo,use a lipo battery and get both
get a hitec 7955 tg and be done with it. they are plenty fast for us averge racers and bashers. and they last forever. just finished my second full year on mine.
I typically run high speed on my throttle/brake and high torque on my steering, but for Buggy you can run high speed on both really. Depends on how reactive you want the front end to be ;-) Anything over 140 oz/in or so should be fine in either slot. If you aren't racing you can get away with a little weaker if need be. Just buy the best servo you can afford. They are pretty important....