I would've said chopper gunner 2 days ago but I've been trying the AC130 out lately and I'll say that I like it better. Sure it has its disadvantages but on the upside.
1) 2 sets of flares and can't be damaged by bullets
2) When called, it's already directly over the map, unlike chopper gunner which takes about 5 seconds to come into full view.
3) Easy multi kills
4) YES you do have to reload but the secret is to cycle through the different guns available, once you have gone through the small shells and the machine gun your heavy shell will be reloaded

5) It flys higher than the chopper gunner, providing a more spread out view of the spawns, that way unlike the chopper gunner you do not have to frantically look about for where they are going to spawn next.