Originally Posted by
Halaberiel
I'll start out by saying, that as a disc priest, pretty much everything works. You check logs, and then players armory, you will find haste/mastery prio works, haste/crit works, mastery/crit works, so as I said everything works. I started this expansion going heavy mastery/haste, for spine HC I went haste/crit, and now on madness HC i'm balancing all my stats.
That being said, it is a good idea to think about the spells you're casting and what stats benefit those the most. You can do this through simcraft fairly easily, and you'll find the following: for single target tank healing throughput (just using shields for rapture) & also for heavy PoH spam, haste > crit >> mastery. This tier has mostly been about casting a lot of PoH, there are very few fights that require shield spamming so I would go with this prio on most fights (Morchok & Yor'sahj HC being exceptions).
The only thing to watch here is that you don't cap your haste, although that's only possible on Ultraxion (with blue) and MDW (if you have Seal, which is why I reforged out of haste a little for this).