Hi guys I was looking at getting some telemetry for my APM2 but havent a clue what ones to go for. RS components have loads of Xbee gear and this is where I would be getting it so wondered if anyone could point out what one to get please. There is Pro,Zigbee and S1 S2 and different antennae choices also. 

I would want a long range option (up to1 KM ) and like the idea of a whip antennae but apart from that I dont really know what else to look for.