I use Towerpro MG995s in my crawler because of the huge torque and metal gear train. The big advantage is they cost me £12 for two of them
. The disadvantage is the positioning isn't too accurate, so they don't necessarily centre in the exact same place each time, but obviously this isn't a problem with crawlers.
A specific problem we have in crawlers is when you run them on 7.2v for the extra power if there's no load on the servo when it centres it overshoots, then goes back to correct itself. With the wheels off the ground it can sit there oscillating back and forwards for 2-3 seconds, but under load when moving on the ground it isn't a problem.