for 6v I like savöx, not that expencive (compared to other top end servos) and has titanium gear.
there are 3 of then to chose from, all of them are about the same price.
SavOx SC-1256TG - Digital Servo 20kg and 0.15 sec/60 °
SavOx SC-1257TG - Digital Servo 10kg and 0.07 sec/60 °
SavOx SC-1258TG - Digital Servo 12kg and 0.08 sec/60 °