Summary:
PvE:
Tested both unholy and frost. Frost does better raid pve (for now).
PvP:
Frost does better dps and is unmatched when it comes to 1vs1 against another melee.
Against ranged and dispels , Unholy does better.
Frost
Playstyle revolves around Obliterate and Frost Strike procs. Also use Howling Blast instead of Icy Touch/Chains of Ice.
Glyph of Howling Blast ( infects targets with Frost Fever on Howling Blast use) is essential.
Priority:
1. Don't miss out on any of the procs.
2. Obliterate whenever the runes are available and you have a proc for crit. If no runes, use the crit for Frost Strike.
3. Howling Blast on proc or when enemy is further away.
4. If both Howling Blast and Obliterate proc are available use Howling Blast 1st.( that way you still have the rune for Obliterate and then when you Obliterate you might get another proc on Howling Blast)
5. Use Blood Strike for the Blood Runes when all other runes are on cd and you also have no runic power.
PvP
Try to maintain the same style of play as in pve when it comes to damage, except you also need to get the Chilblains talent. Your Howling Blast will activate the glyph which will infect your targets with frost fever, and then your frost fever will slow your enemies. So there is no more need for Icy Touch.
Dealing damage when you are not close to your enemy is harder. You need to rely on Howling Blast mostly. Icy Touch, even if proc'd for crit, will still do as much or below Howling. So don't use Icy Touch.
Deathcoil can also be used but it consumes runic power which is better used for Frost Strike. So only use Death Coil if your enemy is at distance and you are full on runic power.
I feel Frost will be even better at 85 when you will also be able to take Desecration (constant aoe slow) from the Unholy tree.
Frost PVP build (final 2 points were between Epidemic(longer diseases) and imp Frost Pres ( more damage)
For pvp against targets that kite you, not taking Epidemic is questionable (keeping blood plague up). I would stil pick improv Frost cus ... mhmm.. cus i just go for all other melees. I would get Epidemic and Desecration at 85.
Frost PVE build
Unholy
The whole ideea on the new Unholy DK playstyle is to use Scourge Strike as much as possible. In order to use it as much as possible you want to get as many Death Runes as fast as possible.
Here are the rules you should follow, in order of priority:
1. Apply and keep diseases up on your target.
2. While BLOOD AND FROST runes are available: use FESTERING STRIKE.
3. While any UNHOLY or DEATH runes are available: use SCOURGE STRIKE.
4. Use death coil when all runes are on cooldown or on Sudden Doom Proc.
Optional: Icy Touch and Blood Strike can be used when their partner rune for Festering Strike is long way from being available.
For pvp you will use Chains of Ice instead of Icy Touch, and most likely you will need to use it alot, thus you will not have enough frost runes for Festering Strike. Use Blood Strike more often in this case.