In Mists of Pandaria, hunter stat reforging priorities have not changed a whole lot from Cataclysm, aside from the addition of expertise. Agility is still king, and is still far enough ahead of the secondary stats to be your most important stat for gemming. The secondary stats (haste, crit, mastery) are much lower and the difference between them is comparatively small.
Here are the Mists hunter stat priorities:
- Ranged DPS
- Hit & Expertise to cap (hit and expertise should be identical)
While the actual stat weights change slightly from spec to spec, the overall stat priorities are the same for BM, MM, and SV — except for ranged DPS which is the top stat for MM.
Crit is the best secondary stat after hit/expertise, and mastery is the worst. Again, the difference between them, especially between haste and mastery, is relatively small. If you respec to crit, and then respec to mastery you would likely be hard-pressed to see the difference on the dummies (due to RNG); however, the difference is there and reforging in favor of crit will give you the highest possible raid dps.
It’s worth noting at this point that the kind of micro-optimization from reforging secondary stats is one of those things that you want to do for raiding, but probably isn’t worth it before then. For heroics you may want to reforge to get to the hit and expertise caps, but that’s about all you really need to worry about at that point.