I was going to recommend that you sub first and try the game with all its perks but. . .
Download and try a few character classes. It takes a month or two to level to 50. In that time you know whether you will like the game, and you will discover whether you enjoy a particular class. If you enjoy it, then sub it for a month or two. You get to see what you were missing.
I bought the game on Amazon during Thanksgiving week for $6!
I'll give it a try with the free month at least, but still diggin' MoP. I also have GW2 and I'd like to try Rift sometime...then there's AC2, Amazing Spider-Man, Sly Collection, Ico Collection, LA Noir, Dishonored, and Fall of Cybertron that I've still got in the backlog.