This is my first time doing any real extensive theorycrafting like this with empirical data. So if my math is off, please correct me...
This is done using a 3.6sec 2h weapon that deals 1k dmg per white hit on the test target. No crits or other abilities are added in the equations to get rid of the RNG factor. The test is done over 10min to the target. This is to give some insight on what Blood and Unholy will do to your white dmg.
10 minute
Blood Aura= 15% dmg
3.6sec swing timer
166.66667swings
1000dmg/swing * 15% = 1150dmg/swing
191666.6705 total dmg
319.444dps
Unholy Aura= 15% haste
~3.06sec swing timer
196.07843swings
1000dmg/swing
196078.43 total dps
326.797dps
As you can see, Unholy Aura just barely passes up Blood. Throw in abilites like Plague Strike and Blood strike- Blood will undoubtedly surpass it in terms of damage. The only weird thing about it is determining how many more abilites you will be able to spam over that 10min period. The reduced GCD is good, but it still doesn't make up for the 15% overall dmg from Blood. The thing about it is the rune cooldowns limit the long term effectiveness of the Unholy aura buff. GCD wont matter when you're sitting around waiting for that blood and unholy rune to pop up. But if we throw in that ability Necrosis ( i believe that's the correct one) that does an extra 25% shadow dmg to melee strikes...
Blood Aura test= 239583.339total dmg (399.306dps)
Unholy Aura test= 245098.038 total dmg (408.497dps)
Keep in mind this is all done without using ANY abilities other than presences. Maybe some of you can add to the testing by throwing in diseases and strikes to determine more of a number determining the dps. The only thing that will help out Unholy is the GCD, which for a DK is not good for dps. You might get off a few more strikes or something in that span of time but nothing to write home about. Maybe in PvP after you stacked up diseases, you switch to Unholy presence and do a burst combo of = Icy Touch-Blood Strike-Obliterate-Death Strike-Death Coil or something like that(That should use all of your Runes) to make that reduced GCD be of some use. But as it stands, Unholy Presence is really weak in both PvE and PvP. Maybe if Unholy reduced rune cooldowns or something else but it doesn't add anything worthwhile. Maybe a beta tester (Theo) can add more insight on it. But Blood is the way to go all around from what I can tell. The threat factor might be a problem because of the healing factor... but there are talents that reduce your threat in Blood presence.