Alright, so I figured I'd just post this here instead of making another WoM article on just specs when really only the PvP DK community cares about that stuff. No fancy names this time around, just the best specs:
2v2:
The best spec for this by far right now is looking like
17/51/3 Frost (played in Unholy Presence) and I'll explain why. Keep in mind, though, that you can easily swap a point from Dark Conviction for Unbreakable Armor if you prefer that; I personally don't think it's necessary.
I tested this on PTR for a while and when using this exact spec and with the gear setup I was using, it is possible to consistently do an exorbitant amount of burst every minute on demand entirely free of RNG for the most part. Here's how:
-I have a base crit of around 37% with horn of winter on. Obliterate has +9% from subversion, +3% from annihilation, +15% from rime, +5% from t7. That puts my Obliterate crit chance at a staggering 69% before factoring resilience, so on average, it's going to be around 58-63% chance to crit a player, and still 69% on a pet.
-Using 4pc t7 (yes, it's viable as long as you use pvp pieces in every other slot), Obliterate generates 15 (base) + 5 (Chill of the Grave) + 10 (4pc t7) runic power, coming out to be 30 runic power per Obliterate.
Therefore, given the Glyphs I used in the spec with free hungering cold and 32rp frost strikes, the burst sequence with full RP and 2 death runes happens like this:
Death Grip Healer and Hungering Cold - 130 rp - 0 seconds (frost fever applied)
Frost Strike - 98 rp - 1 second; 1 rp gained from Butchery
Frost Strike - 67 rp - 2 seconds
Frost Strike - 35 rp - 3 seconds; 1 rp gained from Butchery
Frost Strike - 4 rp - 4 seconds
Obliterate - 34 rp - 5 seconds; 1 rp gained from Butchery
Obliterate - 65 rp - 6 seconds
Obliterate - 95 rp - 7 seconds; 1 rp gained from Butchery
Frost Strike - 64 rp - 8 seconds
Frost Strike - 32 rp - 9 seconds; 1 rp gained from Butchery
Frost Strike - 1 rp - 10 seconds
<Hungering Cold Breaks> - 10 seconds
<Obliterate runes are off cooldown soon here and Frost Fever still active for 5 more seconds>
Obliterate - 34 rp - 14 seconds
Obliterate - 64 rp - 15 seconds
<Frost Fever fades> - 15 seconds
That is the amount of damage you can do in the duration of just the Frost Fever applied by the Hungering Cold itself. If you want to just factor the burst damage during the actual freeze, you're still looking at this:
Death Grip Healer and Hungering Cold - 130 rp - 0 seconds (frost fever applied)
Frost Strike - 98 rp - 1 second; 1 rp gained from Butchery
Frost Strike - 66 rp - 2 seconds
Frost Strike - 34 rp - 3 seconds; 1 rp gained from Butchery
Frost Strike - 3 rp - 4 seconds
Obliterate - 33 rp - 5 seconds; 1 rp gained from Butchery
Obliterate - 64 rp - 6 seconds
Obliterate - 94 rp - 7 seconds; 1 rp gained from Butchery
Frost Strike - 62 rp - 8 seconds
Frost Strike - 30 rp - 9 seconds; 1 rp gained from Butchery
Frost Strike - 0 rp - 10 seconds
<Hungering Cold Breaks> - 10 seconds
That is not counting Rime procs which would be another huge spell usable right at the end of HC on the same second it breaks. Rime also has a good chance to proc in this rotation due to the 3 obliterates (15% chance each oblit). Therefore, you're basically looking at 7 frost strikes, 3 obliterates, and possibly a howling blast all in the duration of a Hungering Cold. Assuming you have at least 1 killing machine proc in there and you deathchill another frost strike (you don't want to deathchill oblit because of its already high chance to crit), you're looking at well over 25-30k damage even on plate just from your own damage not even counting your partner assisting damage (which all healers can now, even paladins with exorcism) unless the other team blows significant cooldowns.
This spec and strategy is viable with any healer really (although I feel shamans will be the weakest with a DK), however, I think of all the healers in 3.1 for 2v2, a Holy Priest will be the best. Yes, a holy priest. Why? Because priests have the best on-demand burst with their holy fire/SWD combos, in addition to spammable nukes with smite and mind blast. Paladins have nothing spammable, druids don't compete either with wrath and they have to leave tree form to do that, and shamans also don't really compare outside of their lava burst combo. In addition to this, a priest's fear does not share diminishing returns with Hungering Cold, thereby offering a very long CC chain assuming the other team's healer doesn't have trinkets up.
Holy priests running a 33/38/0 spec will also be EXTREMELY difficult to kill by having both focused will and blessed resilience, really only losing out on pain suppression and penance. In return, they gain blessed resilience (crit immunity after being crit), much more raw healing power, better regen if you take holy concentration, and most importantly, body and soul. I cannot emphasize how amazing body and soul is. It makes a priest's abolish disease also dual function as an abolish poison when used on themself, removing a poison every tick in addition to disease. Rogue on your priest? Who cares when he won't even be able to crit him, focused will reducing a huge amount of damage, and the priest will be able to easily kite the rogue with abolish and 60% speed boosts everytime he uses PWS. I've tested this myself on TR playing a priest and it's much better than I thought it would be.
Dark Conviction and 2-handed weapon spec also supplement this spec extremely well because of Frost's dependency on crits and the fact that 2h spec benefits obliterate, frost strike, and all white damage that you do.
3v3:
A lot of people can't hand-pick their perfect 3v3 comps that they want to play so the best spec for this will largely depend on what partners you have available but typically speaking, due to the nature of 3v3, I think an Unholy Spec will be stronger due to the amount of collateral damage going around. However, there are exceptions to this. If you play a comp that revolves around single target burst and CC's that don't DR off each other such as a mage/priest/DK comp, then I feel the previously mentioned Frost spec will be best.
When playing with most other comps with classes such as any physical dps, warlock, etc, I feel Unholy will have the edge with its higher sustained damage output. The spec I find to be strongest is this
0/19/52 spec played in Blood Presence. Some people will probably ask about the point allocation and glyphs so I'll explain a few of it:
-Many DK's got used to the old ShadowFrost playstyle with glyphed Icy Touch giving a huge source of RP. With this spec, the main method of applying Frost Fever becomes Chains of Ice. With the Glyph for it, in my gear, CoI hits for about 900 damage everytime. The problem is that CoI has no glyph for increasing RP gain, so to help remedy this, I picked up Chill of the Grave. Without CoI glyph, you'll lose a good amount of damage because your blood runes will basically be doing nothing and neither will your frost runes, leaving all of your damage to plague strike and scourge strike, which isn't exactly the best idea. I also decided on Improved Icy Touch over 3 points in Toughness because Toughness is pretty worthless without Bladed Armor and the extra melee de-haste from imp icy touch actually does provide some benefit.
-As much as I love Wandering Plague (would still get it for 5's instead of chill+amz probably), I just don't feel there's room for it in a 3v3 spec when there's so many other "necessary" talents.
-Improved unholy presence is just bad. Unholy presence is also a bad presence to use as Unholy because you're not limited by your GCD's like you are with Frost or Blood.
-Glyph of Disease is great when combined with Reaping. There's not much else better to use your blood runes on than pestilence and especially in 3v3, teams often don't have the globals to dispel diseases (and pets totem stomp DCT's), meaning your pestilence refreshes will be much more useful here.
The rest of it should be pretty much self-explanatory and 5v5 specs are entirely preferential and 5v5 is pretty homo to begin with so I won't really cover that. If you have any questions about these, feel free to post them and I might be able to answer them.