The quicker you cast the quicker you get into Meta, the question is, is it better to stack haste and get into meta quicker or to stack mastery and hit harder when you do get into Meta? Let's hope as new tier's come out and stats get better it becomes more obvious!
Depends on fight mechanics. For Gara'jal for example, I'd go with Mastery for sure because of the insane buff you get from going into the spirit realm. For Elegon I'd also go mastery because you can build it up on pillar phase and blow it all as soon as you get back in. Any fight with a damage increase that's not there all the time or stacks over time definitely favors mastery builds.
well in my current gear, ive simmed crit to be worth the least around 1,3, mastery at 1,5 and haste at a whopping 1,9 and int at around 3,7, so for me haste has taken over mastery's job from afflic which is quite odd, since everything i read says that for demo everything is about equal, but my sims doesnt support that tho
Personally I reforge for hit > mastery > haste > crit - this suits my playstyle of pushing as much dps into my meta phases as possible. I find that if you manage to plan your fights adequately you can have enough fury when you want it (for heavy movement or burn phases). Using wild imps to boost your fury at the right times helps a lot with this too.
I am still at a fair amount of haste however - and may play around with a haste reforged setup for spirit kings hc etc.