Not sure if this has been mentioned already but..... When your doing a mission which has the normal maverick helicopters that spawn after you pick up the package, just take out the shooters and leave the helicopter pilot alone, NPCs neutralized.
Also Hydra + Nightshark for the win. Hydra can land and take off like a helicopter but can also outrun or out maneuver whatever comes after you. The Nightshark takes a beating and the f*ckers can't blow you up in that thing or if you're not running solo, take your custom Insurgent and have a gunner on back.
Missions are a walk in the park so long as you have your armored vehicle ready to go, before you grab the package, making sure you don't trigger the angry NPCs until your ready. haven't dropped a supply or sell mission yet.