A quick note to help clarify something obvious. Cataclysm has totally changed the choice of which presence to use. We are in a new and highly logical world where the two choices are Frost or Unholy. Please do not use Blood Presence for DPS any more, its a Tank Presence now.
Update 26-Sep-2011: Use Unholy presence for DPS. The rest of this post is based upon old information, and has changed. I would not expect an update to this now until after patch 4.3, or even in the next expansion.
From now onward the choice of DPS presence is between Frost and Unholy. Generally if you are an Unholy DK, then use Unholy Presence especially where fights require a lot of movement. When doing AoE where you have time to switch out of Unholy, and will not be moving back to single target quickly you can switch over to Frost Presence.
Also if you’re a Frost DK then use
Frost presence for dual-weild and Unholy for using a two handed weapon (see links for proof). This is a deliberate change in style so that the spec matches the presence. So the DPS rule is now: 2h weapon = Unholy, x2 single handed weapons = Frost.
I posted a long time ago in Wrath about which presence to use, but that post is now totally out of date. I’m posting this now because my old post still gets a lot of traffic and it needs to be corrected, and also because I’m starting to play a DK again and I’m having to retrain myself as well. Heck – I still switch to Blood sometimes by habit.
Apologies if this is stating the obvious. Happy Killing.