Are you just turning it on and off, not sending some limited current? If so, I'd go with an N-channel MOSFET, probably a logic-level one. (A regular MOSFET needs ~12v to turn fully on). Pick one rated for ~4X more current than your servo needs. A MOSFET will offer virtually no resistance when turned on, whereas a BJT will drop ~0.7v across itself, and will also require a base current.
We must make a Electronic barrier arm using a Servo.
We need to use an LDR then through the picaxe we need to open it when the LDR is shaded and close when it is not shaded.