None of the specs give AAs. They all give SPs and TPs.
And the best ones are anything except Stalker. Some of them only work in certain game modes like Tracker and Engineer only work in game modes with ordinance drops and none of them work in game modes where you can't choose your loadout.
Pioneer will give you lot of extra experience if you unlock it early but it gets less useful the more specializations you complete, so I recommend you do it first if you're planning to grind all the specializations as quickly as possible. If it gives you any bonus EXP at all though I still say it's more useful than Stalker.
I recommend doing Pioneer first, Stalker last (or next to last if you don't want it to say Stalker next to your name forever), and then choosing the middle specializations based on what game modes you like to play and how you play them.
Obviously somebody who hardly ever touches a vehicle isn't going to want Operator anytime soon, but if driving is your thing then you should prioritize it. If you use scoped weapons a lot, Rogue is the spec for you since it will stop counter-snipers from staggering you. If you always find yourself wanting particular ordinance but the damn game keeps giving you Needlers, give Tracker a shot. If you like stealing ordinance then Engineer is the obvious choice. If you hate it when your stealth gets foiled by footsteps or promethean vision, you want Wetwork. If you often jump into the back of warthogs, hop in the gunner pit on a scorpion/wraith, use mounted turrets, or rip out said turrets and run around with them, Pathfinder will help them not suck.
Is there something about the way I type that makes it sound angry? Maybe it's just something about the way you read.
Operator and Pathfinder are good ones to get back-to-back if you're someone like me who enjoys using vehicles. Getting the Wheelman perk from Operator is a definite priority, especially if you end up using a lot of ghosts. Those things are extremely annoying with Wheelman.