I've been having good luck with Dymond 4.7 servos in a couple of 1/2A planes the last few years. Small, light, strong, reliable(so far), but not the cheapest on the market. Been satisfied with them enough that I've bought some smaller 3.7s and larger 6.0s to use in slightly smaller and larger glow models in the near future. I've used lots of HS-55s in 1/2A planes over the years but have had to replace at least a handful of them. Never lost a plane due to a failure. They just got to the point that they started quivering at the neutral position. I always pulled them from service when I saw those symptoms. Still have some in service, bit my newer stuff is flying with HS-65MGs or Dymond servos. No failures so far.