Originally Posted by
Katarn
The OP's question was legitimate, and it was answered quite well.
The rest of the mouth breathers that came in here with no idea what they're talking about and start saying random things tend to piss me off.
But for your benefit I'll go a bit more in depth.
In TBC PvP gear was largely BiS because it had the most Bonus Armor (a few exceptions), and Resilience was much, much easier to come by in order to get the crit reduction you needed.
In Wrath PvP gear was BiS simply because it had the most Stamina, and the most sockets (which meant more Stamina). That's it.
In Cata PvP gear operates 6 item levels above the the relevant tier. That is while PvE went 346 -> 359 -> 372.....PvP went 352 -> 365. At launch the PvP 4pc was actually BiS at the 346/352 level because the 4pc used to be 180 Agility. That combined with the extra Armor (and to much lesser extent Stamina) made up for the relatively insignificant secondary stat loss. Especially since at the 346 level secondary stats that weren't Dodge or Mastery weren't worth very much.
Pretty early on the 4pc was nerfed, and 346 PvE gear was slightly better than 352, with the exception of the 2pc. The 346 helm and shoulders were pretty terrible, and the 2pc PvP bonus made up for the secondary stat loss to Resil.
However this is no longer the case for any sort of relevant content - defined as current tier normal mode raiding. The sheer amount of secondary stats you lose (plus any applicable Agility socket bonuses) on a BiS PvE piece more than makes up for the (minor) difference in Armor, Agility, and Stamina. The only cases where this isn't true is where you have a Hit / Haste piece because Haste is virtually worthless except for reforging into Dodge, and while Hit is worth more than Haste, it's not enough to counterbalance the Agility / Armor gains.