When I say best I mean easily soloed, relatively short and pays well. I've been doing Coveted but killing the same two dozen goons over and over is getting too repetitive.
you dont have to kill two dozen goons. you only have to kill 6-8.
when you start, snipe the guy by the granger. then run down to the granger, but keep to the right.
hop in the granger and reverse down the hill a little bit (on the right). then turn it around or just reverse down the hill toward the enemies (near where the helicopter lands).
as soon as the the helicopter starts flying, hop out and snipe the guys at the bottom of the hill. it should only be 6 guys. after that, 2 may run over the hill.
wait for the helicopter to land, and kill the pilot when he gets out. hop in the cargobob and proceed to the container. you will take a lot of fire while picking up the container, but the cargobob can take it. im pretty sure the glass is bulletproof as well. its usually spewing smoke while im flying to madrazo's but it has never blown up on me.
i use this method to beat coveted in about 3.5 minutes, only killing 6-8 guys every time