... why are you using in-game script links?
Just link to the wowhead page.
I'd go with the resistance one anyway, the amount of parry/dodge you would gain from the str/agility is negligible.
Might be hard to put the combination of mastery (physical/melee mitigation stat) and resistances (magic mitigation stat) to good use, though.
the Mirror of Broken Images is the best, getting 1.76% parry or 3.84% dodge for 20 secs every 2mins is worthless compared to 400 resistance every minute for 10secs. Also the cooldown and the amount of time it lasts is same with our Divine Protection so I macro them together and pop them when I'm taking dmg.
The mastery trinket is, without a doubt, the best trinket you can get from Hellscream's Reach. Alot of the damage ingame at the moment is spelldamage, and mostly it comes in bursts, and when the trinket brings you up to around 45% (with aura) on a 1 minute cooldown, there shouldn't be much confusion about which one to pick.
The mirror was the first thing I bought and it made Nefarian a good deal easier on the healers during the shocks, like its been stated tons of magic damage in that fight and in general this tier, the mirror along with glyphed 40% magic reduction provides 2 great magic CDs for the nefarian fight if you stagger them. That teamed up with a CD from your healer and you can reduce every single "Crackle" as we call them in my guild. Your healers will love you for it. Highly recommend for both tanks that fight to have one. The best part of the trinket is the static mastery and a magic reduction...best of both worlds in my opinion.