Hitec HS-7955TG. It costs a lot, but you will never break it. Buy once, cry once.
Everyone says you need an external BEC to run a crawler servo properly. You don't, not as long as the internal BEC outputs at least 6V. If the servo seems to struggle running on the ESC's internal BEC, or if you intend to operate the vehicle in conditions where the wheels will bind-up in crevices and you still want to be able to crank them to the side (because you hate your vehicle, I guess?) then you need an external BEC, but other than that the internal one will be fine. Hardcore crawler guys will disagree, loudly and insultingly, but that's because they like to overbuild everything. I've been running my HS-7955TG in my Wraith on the internal BEC for two years and somehow, miraculously, the world hasn't exploded even once.