Farming HQ can be very costly, as you are purchasing a spec, a minigun, and possibly more. It used to be the #1 farming method a year ago, however playing Arms Race on Junk Flea gives much faster results and possibly more EXP. (I don't know because I don't do HQ anymore) I got from MAJ 1 to MAJ 3 in about two days, spending just a few hours of playing Arms Race with a 500% EXP boost. I earned about 6-8% per match, and each one lasted probably 15-25 minutes, probably less.