First, what's been said: Nibuca has a great post up right now. A lot of what I'm going to say is based on what she's already written, so obviously I agree with it. It's key to note that her advice is a bit different from the message I've seen delivered by more theorycraft-heavy sites. The meat of the discussion can be found here, on MMO-Champion, if you're interested in delving further.
Perhaps, I'm getting ahead of myself though. Most people, especially if they don't have a 'lock, don't even realize we have a new buff. I feel like I need a clever macro that whispers someone to let them know I've DI'ed them. Even then, I'd get mostly blank stares and grunts. "Buffed me with something? A Lock? Thanks... I think."
So what does DI do? Well, the base is a 3% haste buff for you and the target. Good stuff. You get that no matter what. The tricky part, then, is the little bonus that doesn't show up on an icon mouseover. Very simply put, every time a DoT or HoT tick crits for either of the DI'd folks, you will gain an additional stacking buff (up to three stacks). This bonus buff simply increases DoT/HoT tick size by 3% per stack. So either your heals get bigger or your dot damage gets better.
What this means, though, is that there is clearly a need to choose wisely in our buff target. As Affliction locks, we're already in a good place due to our extensive use of DoTs, but not every class is so fortunate. The old adage "two heads are better than one" certainly applies here. The more DoT ticks, the better your chance to engage and stack your bonus buff. Thus, we want to maximize our chances.
It would seem very simple then: pick the biggest DoT/HoT user available. Indeed, that is what the advice from theorycrafters seems to center around. Yet, what Nibuca (and now I), argue is that we need to be smarter than a mere table. All fights are not created equal. All groups are not created equal. Depending on the roll of the dice, we may need more help healing on one fight, and then DPS'ing on the next fight. Or, maybe we're consistent through one run, but not night to night. The bottom line is, we'll need to judge for ourselves.
Nibs advises that we look to DI a healer first, until DPS becomes a problem. As such, she lays her priority out like this:
- Resto Druid
- Holy Priest on the Raid
- Resto Shammy
- Holy Priest on the Tank
- Other healers.
- Shadow Priest
- Fire Mage
- DPS Druids (Kitty, Boomy)
Therefore, my priority looks something like this (All things being equal. That is to say, when there is not a clear deficit in either healing or DPS'ing):
- Shadow Priest - This should be our best bet with our dotting brethren of the shadow.
- Resto Druid - Is anyone hottier?
- Fire Mage
- Boomkin - They call them Crit Chickens
- Kitty Druid
- Holy Priest - I'm not going to bicker over assignments.
- Resto Shammy
- Survival Hunter - I often run with one of these.
- Frost Mage - They have a DoT from Frostfire bolt.
Also, you're notice that nowhere on that list is another warlock. That would be a waste, since the buff does not work to the fullest extent on one another lock. They just don't play well together right now. Don't do it! Just like when a guildy whispered me last night that he was running with a lock that was making extensive use of his blueberry in a dungeon... I will facepalm at your expense.
Whether you prefer the more healer-friendly approach of Nibuca or my more selfish approach, you should most definitely give it due consideration. As you learn raids and boss fights, you'll want to note which ones the healers tend to struggle on, and which ones you could benefit from increased DPS. Make an informed choice, first!
I feel I must also add that if a Mage is ever beating me on the charts, I will purposefully withhold DI from them out of spite. Not that such a thing has ever, or will ever happen. Nope. Nevah.