I would stay away from the JR 9100s. I have 2 and they both developed alot of slack in the gear and they both do the "death rattle twitchy thing". One twitches more violently than the other. I'm going to send both of them back to Horizon and get them replaced then Flea-bay those turds.
The best steering servo I've ever used is the brushless Futaba BLS351. I've got over a year on it in my MBX5R and there is absolutely no slack in the gears and it has always worked flawlessly.