Servo choice depends entirely on what you will be using it for; that is, how much speed and torque vs. $. The RF168 will work with $10/ea servos up to $150/ea servos. The model decides the need, not the transmitter or receiver.

I like HiTec 605/635 for rudder servos and Futabas for all else in my .40 & .60 size models. In my gas models I use Futaba digitals, cored or coreless. In all I use a "cheap" Futaba S3001 or S3004 throttle servo. If you mix brands just make sure the connectors are interchangable.