2 air is never ideal. You should never have more than 1 air player, up until late t1, at the stumpy/hlt phase of the game (Where people can get air as second fac but shouldnt reclaim their first fac for it).
Airdrops are ideal on porcier maps where the enemy has a single chokepoint where most of his defenses are (Altored especially).
There are four main types of airdrops:
The base drop. The enemy is not expected air and has no AA. You unload your units directly into the middle of his base and tear it up before he can react. In this case, always scout directly before your atlas's go in, while they are waiting with their load just outside the target area, ready to go. Every second that he knows you have air is a second he can use to get AA up. If your scout reveals he has AA in his base (Despite you not having used air), just change tac and go for the second kind of drop.
The back drop. You have used gunships, bombers, or have otherwise given your air away, so the enemy has put AA over his base to counter this. However there is still a section behind his base (Perhaps even his windfarms) which has no AA where you can safely drop. With this drop you can afford to scout meticulously well before the assault, as he is already expecting an air attack.
If he survives this kind of airdrop, he needs to place AA in any position you might be able to drop from (All along the hills in altored or charlie). This takes a lot more resources and spreads the AA a lot thinner than just putting AA around his base.
The Commander ambush drop. In this airdrop you drop your units around his commander, surrounding him, then you pick him up with the now empty atlas, preventing him from d-gunning (Or, against an inattentive player, napping him). On com ends, this is devastating. Note that comnapping is lame and if you do this in most team games you deserve a whuppin'.
Com/Con drop. To rapidly secure an area, drop your com/cons early on and get defenses and a kbot lab up. Favourite tactic on tabula. You can also drop your com near his base, but doing this against any good player will make them make some AA so you cant get conplanes up there, then combomb you and reclaim it. You were asking for it, if he does this.
(warrior drops are saktoth's favourite)
Warrior drops are sefidels favourite. I also enjoy warrior drops but i am not 'Oh god, he is going to try and comnap us and use drop warriors again.' the way sefi is.
