Launchers: Attack choppers, chopper gunners, and gunships take two hits to down, as your first "hit" is technically dodged/chaff. It does not matter if you use a Strela or M72, the fact that two hits are needed remains. You can target choppers as soon as they are visible making the first hit, the dodge, capable of being logged without the attack/gunner/gunship firing a single round.
SAM turrets: Useful, if your team mates are reluctant to help with anti-air. However, they place their priority on what was in the air first so if the air is full of enemy spy and counter spy planes, they will not be of much use in downing the chopper quickly (bonus: they are capable of hitting Valkyries). Downsides are their limited lifespan (1.5 minutes) and their ability to be destroyed or hacked.
Concerning attack choppers, you can down them in one hit with the RPG, but the weapon is unguided and inaccurate at range, making it a poor recommendation.
Care package helicopters can be taken out with one hit, if you are able to get a lock on the chopper fast enough, its destruction can result in the opposing team's care package to be dropped out of bounds, eliminating that kill streak reward.