The 601 with a 9251 servo would be the way to go if you have the money, if you don't, I would go with the 401 with the 9254 servo. I have had very good luck with the 401, it holds rock soild and it is easy to set up. I'm going to try the 601 on my new heli. I have read a lot of good thing about it, people seem to like it a lot and say it is one of the best gyro's on the market.