Anyone who is serious about professional servos should check out Dynamixels. I say professional because they are way overpriced. But, They now sell a $49 version that fits the form factor of the other X models. I have one which I will post the results here.
Here is the reason I sing their praises. I have three dynamixel MX64AT's inside Alan, two which control his up and down on his head. I have been doing endurance testing on them. They have been holding Alans dead weight head which is about 6 pounds (aluminum version) for 17 days non stop. To be clear they are on and in their 0 position so they are holding that weight, no sound, no heat for 17 days/24 hours a day. Its amazing.
I am very curious about the X brand I have now. They are much smaller than the 64's. About 1.5 times the size of a standard servo, with all the resolution and PID feedback etc.