The Shuttle Z/ZX does not have the collective range etc. to be an extreme 3D bird so for sport aerobatic flying, which would be the most demanding type of flying I would assume yuo will probably want to do with it,

The important thing therefore, is to insure you get dependable servos that can take the extra vibrations of a nitro heli over the long term, while remaining relatively precise, with adequate power. There are many such servos on the market that will do the job admirably without hitting the wallet very hard.

My favorite for 30 size helis are the Futaba S-3151 digitals - dependable and relatively low cost.