Bounties and strikes were my preferred method on all 3 characters. It moves rather quickly as you progress through the playlists, but you won't get full level 20 blue armor until you're doing the 24 strikes. The faction with the most benefit right now is vanguard, so don't equip a reputation cloak and just keep working on it. By the time you get rank 2, you'll have the points to buy a few pieces and rank 3 offers legendary guns.