Look on youtube for some of the MP footage people have posted. The AC130 is good, but the chopper gunner is much much better because the gun fires much more rapidly with no reloads. The AC130 is so high up, the bullets take about 2 seconds to reach the ground, you have to lead your shots.
From what I've seen so far, my setup is going to be:
UMP 45/ Bling. (Silencer, red dot)
Stopping power, Ninja (Dead Silence).
I'll use the pp2000 as my side arm. Pretty much a skorpion from COD 4.
I'll use chopper, pavelow, and chopper gunner for my three killstreaks. BTW the pavelow is just like the regular chopper, only it has armor so it can withstand a rocket or two.