We've run several of the ser vos mentioned.. the KO, the Savox, the Sanwa, and all three Futabas. While I can't really say anything bad about the KO and Savox servos, we kept going back to and finally stuck with the Futabas - they just felt the best on track. The Sanwa SRG was very similar to the Futaba, but imho not worth the higher price. I run the BLS551 in my TC's, the Mrs. runs the 9551's... same lap times with both, both great.