Personally, I use Futaba full size servos in my nitro planes and helis, and Hitec HS-55s in my micro electric planes & helis.

It's all a matter of opinion... I like the Futabas because I know that family of servos pretty well, and know which ones I like for different applications. I've also found them to be pretty rugged & reliable. The HS-55s are probably the most popular sub-micro servos for foamies and micro electric helis.