I was on howtopriest.com, used to be shadowpriest.com, and it was saying crit > Mastery but according to noxxic, it's Mastery > crit. I just got back into the game after a long break and was wondering about stats.
Mastery is the best single-target stat (CoP), but it is the WORST multi-target stat (AS).
Crit is a good single-target stat and the BEST multi-target stat.
Best + Worst < Good + Best
Added to that is the fact that the better your gear gets, the more of an advantage AS has over CoP. As crit levels increase, AS may even surpass CoP in single-target fights (or at least come veeeery close). Of course, BRF also happens to have a lot of fights that benefit AS, so there's that to consider.
TL;DR: Gear for Crit, it works best with both specs.
Ultimately you use what you have. At low gear levels, the higher ilvl piece is often better regardless of stats. I don't think I'd go more than 5 ilvl lower on an item just to get the right stats (if even that).
That being said, I see you're speccing into Power Infusion. That's usually not a very good choice.
Anyway, with BRF in the mix now it's perfectly safe to just gear for crit. In HM CoP was very good on most fights and crit levels where lower all around - now that they tend to be higher, crit is where you want to end up. However, the difference is fairly small - and since you seem to only be doing LFR for now, CoP might very well still be the spec of choice for you because your overall crit might be too low for AS outside of heavy multi target fights (e.g. Beastlord).