First question are you horde or ally.... if your Ally: Shoulder, Weapon and then Chest... 'cuz you can satisfy the hit loss as of horde can't ... as Horde you only buy: Weapon and then Chest 'cuz you should stay hit capped then rather have a little more crit.
About the PvP vs the PvE ones it depends I'd preferly take the PvE Shoulders rather then the PvP Shoulders 'cuz with the resil and more stam they are better for FCing IMHO.