For me hands down a quality core-less digital servo is the best bet.
I went from using hitec 645 mg to jr 8411 and it is a night and day difference. My 645's center would drift with a varying supply voltage say 5.5v to 5.0 gave me about five clicks of trim to bring it back to its center. no to mention the speed and accuracy.

My recommendation is to spend a little more (well allot more.)
and get the jr 8411 . You will not be disappointed.