There are three rows of chests, each row has a class symbol on the floor, you go to the symbol of the class you want armor for. As pointed out by other people here the armor chest for Hunter have a blue glow, Titans have a red glow, Warlocks have a yellow glow. Your going to need a lot of medallions to grind for again. I got all but the Titan helmet for my Titan and I accidentally just got the Warlock helmet just now, and now I need to go get 50 more medallions, I shall know your pain.