What killstreaks do you use and why?

Spy Plane, Napalm Strike and Chopper Gunner.

Spy Plane gets me more kills than the RC-XD, and they count towards my next killstreak as well, plus it helps my team out.

I was working with mortar team until I got sick of getting 0-1 kills even on nuketown. Napalm is good for area denial as well

Chopper gunner is fantastic on TDM when your team is behind. Even one of them can turn the game around in your favour.