Mainly from a warlocks point of view I have farmed MC for a long time and am moving into BWL and our guild has high hopes to move beyond and are moving rather quickly. The question I have is with the better and better gear that is dropping I am having a harder and harder time deciding which exact pieces of equipment is better from a math pespective. I know there has to be some way to decide which is better for a pure DPS standpoint...I consider that 1% to hit is equal to avg Shadowbolt dmg/100, and same for the most part with 1% to crit. But it seems there are also a lot more factors that come into play as with how much stam/int is needed to go along with that, should it just be ignored completely and go straight for +dmg/crit/hit? Also since alot of the higher end fights have adds that can be dotted crit seems to lose a lot of value and in turn makes +to hit more valuable since dots are binary?
How are the warlocks in EJ/other guilds into BWL/AQ40/Naxx deciding exactly which pieces for each slot to choose?
I'm not an EJ Warlock but I've farmed BWL sufficiently to hopefully be able to answer your question.
During all of our time learning BWL, there was not one point where I felt like more hitpoints was what I needed. I looked at every upgrade from a pure DPS standpoint, and took the stamina/intellect increase that came with it. Now, after having raiding a while, I've put together three sets of gear outside of resist sets:
-DPS gear. Randonm mix of non-set gear like Mish'undare and Ebony Flame gloves. This set has 3/8 Nemesis because it's just plain good for DPS with the bonus
-Aggro sensitive gear. 8/8 Nemesis and Fetish of the Sand Reaver
-Survivability gear. Nefarian Neck, Brood of Nozdormu tank ring, Dragons Blood cape etc.
I use the DPS gear for all of MC, all of BWL (minus Broodlord) and most of AQ. I use the aggro sensitive gear on Broodlord and when we're learning fights that aren't easy to tank (this was huge on Huhuran while learning, now I just go DPS gear as we've gotten TF since and so on). I use the Survivability gear while learning fights with lots of non-resistable damage going around, and/or on trash mobs where for one reason or another, I'll be taking damage but can't rely on heals. This has come in handy in Naxxramas especially.
To sum up though, if you're not blind, you'll be able to do just fine with just the DPS set until well into AQ or possibly into Naxx, so if I were you I'd focus on that first.