You'll want something with at least 100oz/in of torque and around .12 sec./60* transit time. A servo is one of those purchases that you can make one of two ways: 1) save some money now by buying a less expensive servo and then upgrading to a better (= more expensive) servo later, or, 2) waiting a little longer to buy a better servo now and saving a little money in the long run. Your call I always try to take option 2.