I just got the Daddy War Bugs achevement, and when I got tired of using the Jet, I used the Trooper. He has a ROCKET launcher, not lock-on missile launcher, that will track several targets at once. It says something about it in the description, youll have to read it, but thats what I used on Inferno.
Its a pretty powerful weapon, it does an Air-Burst, and looks like it tracks 5 or 6 targets, and does big splash damage. You dont have to worry about the AI bots stepping in front of you since you can just look straight up and fire it too.
I did all PLAYING farming on 3-3, and all rubber band farming on 1-1.