Updated with the crafted legs and belt.
For hunters who wont see heroics until late in the tier, the crafted pants look BiS and the belt is awfully nice also.
BiS off-piece is indeed the legs. Especially since we are going to need the expertise on shoulders since we will drop renataki and hit from the purple gems in the legs since we will have so many red and orange orange (as an example, compare sockets on t15 and t16 chests).
I did consider helm as a possible off-piece when the tier helm's socket bonus was 180 crit instead of 180 agility but now it's definitely the legs. Even with a haste > crit you are getting so much more crit from using the off-piece legs over the haste/mastery helm that it overweights the haste.
Updated with BoA Bow off Garrosh....
These posts make me cry of impatience!
When the silver shining moon meets the roof of the trees,time stops and listens to your weak heart's beats...
With first wing of LFR and 1st two wings of Flex now open, I'm bumping this back up for people who might've missed it since it was discussed pre 5.4
(I don't intend on bumping it often, maybe just once after each new wing is opened -- Mods please let me know if the occasional bump is not allowed)
BoA Bow from Garrosh is BiS unless you can get a Warforged one.