sentry turret + pave low do not count towards your kill streak
the rest does.
even the harrier *after* the airstrike helps you to reach your next kill-streak, which is why I believe this perk is a must have... 7 kills -> not difficult to reach, once you have it you might get 2 or more kills out of it -> AC130/Chopper gunner -> ~10 kills or more possible -> nuke
I'm not sure if the predator missle will add kills however
well the ACR takes like ~2 seconds to reload and faster ADS doesn't really help with that weapon... and because I don't want to change my weapon which has, with no doubt the best accuracy I'll need scavangerI prefer Sleight of Hand over Scavenger because if i run out of ammo i pick up enemy's weapon, and faster ADS from pro saved my life many times.
it allows you to spray into windows etc a lot more too
it's not really rare that I get 7 kills and ~5 from it were through a wall with the help of a UAV.
ACR is a reallybeautiful weapon, once you hit the enemy, it's impossible that ur other bullets will miss and it's impossible for the enemy to hit *you* because of it's high rate of fire. (his crosshair will literally jump to the skies)
picking up stun-grenades and semtex is nice too, especially when playing HQ
edit:
oh btw
killstreaks won't count towards your kill-counter if you get them -> die -> respawn and activate them
you have to use them in the same "life" if you wish them to count... however that's not always a good thing to do because it takes a while to activate some of them :P