Sniper Helo is nice, but if there's a player with even half a brain on the other team, they'll get a Titan w/ FMJ 2 and shoot the Helo down or a sniper and just shoot the snipers out (which you can do, in one hit for each sniper). In open maps, the Warthog is good. It's difficult to shoot down, and generally will keep player's heads down. The attack chopper is pretty much the same story, but much easier to shoot down (especially if someone has a decked out launcher i.e. Fast Lock, Speed Loader, Extra Rockets, etc.). The Dart is actually surprisingly effective - very maneuverable, pretty good explosive radius (you can get a few triple or double kills if you get a nice grouping of enemies), and it's harder to take out than the RC. Strike Team sends in literal Foxtroting terminators that'll net you quite a few kills. Gunship is fun, but if the enemy team just manages to hide inside for the duration then it's a waste (still the most fun streak tho). Lightning strike is only good on open maps with little overhead cover and only in objective modes tbh. Mantis is alright, but the AI is shit since Cold-Blooded counters it - just control it, it's more fun like that anyway. And last but not least, the Sentry - it's OP and unless they have a Zero on the other team, you should def use it. Set up in a good location, it'll net you a good amount of kills or at the very least it'll lock down a few sightlines while you keep your attention on others. As with other streaks, Cold-Blooded counters the AI but only partially - just gives some extra delay for the auto-targeting. Good in Hacienda, Nuketown, and a few other maps that have good set up spots (especially when paired with shit like Torque and his entire bullshit kit).
Dii rax los zahkrii, dii jusk los niigol, dii viing los suraghol.
I'm too lazy to do the math but the Mantis is godlike. It's gotten buffed twice so far, too, IIRC. It's not as good as the Cerberus was in BO3 (which got buffed almost every patch) but boy. BOY. Sniper's Nest is also amazing. I don't know why the Attack Chopper even exists, it gets significantly less kills, is easier to take down and it's like 200 points more expensive. Real shame about the Drone Squad, I used to use it closer to launch and it was pretty good, they must have changed the AI at some point because it never gets kills anymore. I've been running UAV/Sniper's Nest/Mantis for months now.