Overall best aa is stockpiled screamer. Can kill mass bombers with one two shoots. Kill licho with two shoot. Even krow fear screamer. And its range is awesome.
Chainaw is best general static use aa. Large range and huge hp. With support mobile aa it can kill most air units.
Razors is cheap meatshields but they works pretty good vs slower gunships.
From air units swift in large maps, vamps (hawks) in small maps. Tridents with rapiers ir very strong combination as aa. Licho can be used as aa (wyvern) because you can licho entire hawk ball and also gunships. Ravens perform also pretty good vs enemy gunships and even krows. Krow also can be used as limited aa and kill swifts or bomb hawks. In clise combat rapiers is OP as aa. They eats swifts and can kill hawks. So need hit and run and hawk have range advantage over rapiers.
From mobila aa i think best is is archangel in overall terms.
Crasher can be epic aa as well when in mass and with its super fast speed it can get most aa especially krow flying away. Plus crasher best ability - big alpha damage and fast missile. So you can shoot and run away.
Tarantulas range is pretty good. However its speed is poor and even all terranain ability didnt help.
Gremlin is inivisible and for more sneak attacks. One of most poor aa and i have seen small games where they decided. I speak abut team games. Gremlin plus is its insta hit. But they range is so close and that sucks.
Vandal is cheap meatshield and with player who is intensive micro specialist they can become pretty good aa. They arent good aa when clustered by newb so licho can hit stright in ball.
Vandal and gremlin is very agile aa and can evade even two brawlers in same time. I have seen it when gremlin dances and kills.
Copperhead on paper is strong but in practice its isnt so immpresive. It have tendence to miss its target. Plus is need flat ground.
Flail is strong in alpha dmg but it launch its missiles so slow that enemy already can bombed your com/target and got advantage even if lost his bomber(s). However its missiles can fly pretty large range if target is seen.
Angler is interesting unit with 4 missiles but its range is bit too low maybe. Better prefer on land then on water.
Ship aa Shredder is innacurate. Expensive. Cant deal wits raven swarms or licho.