the absolute fastest way to do this is through vanguard armor. Get your reputation level up with vanguard bounties, your weekly, and systematic patrolling. Strikes give you I think at the highest level, which is 26, but they are considerably slower than patrols. Patrols give you from 10-25 reputation in a matter of seconds to minutes, whereas a tiger or ROC strike gives you 25 reputation for something that takes around a half hour, depending on your group. If you get a fire team of 3 in the cosmodrome and spread out into three major areas, you can get several hundred reputation an hour. This is one thing I can actually say that I am pretty much an expert from experience with. I went from lvl 1 to about 28 in a few weeks. Obviously now I can do that significantly quicker, but that was my first character coming into the game completely blind. Something definitely worth doing if you have the time, if you are playing while the bounties drop each night, you can actually grab them and shut your game off and they will reappear the next day, or whenever you sign back in.