Currently the general consensus is to stack Crit for an RPS build. There are a few still using a mitigation build and there is discussions on how a haste build could be beneficial, however this seems to stay in the 25m raids.
Overall most stats sound like they are going to stay similar in 5.2 with the note of maybe needing 2 sets if you Heroic raid.
"...when dealing with Melee damage you will want to stack Haste/Mastery pieces after Hit/Exp capping in 5.2. This means that you will end up building more than 1 tanking set if youre a heroic raiding Guardian. One for RPS/DPS, and another for mitigating pure melee hits."
Tiermordius on Nathrezim Server (US)
Main Tank for Pride and Ego