I think fastest is a combination of pvp and arena. Buy some honor pieces, and some honor/arena pieces.
And there's another benefit of pvp:ing for the gear.. you practice your pvp skills a lot, which will come in handy in arena later on.

If you just go pve heroics, you won't be accustomed to dealing with gangups of 10+ players.. which is good practice for arena.


Going against 10 players in a BG has a similar feel to it as going against 5 players in arena.