That's only big deal for prot players :P I have no issue taking ele / sp / arms and play frost. I qualified for MIT3 playing sp / frost dk / hpal, went unholy for the tourny.
Played Prot / Frost DK / hpal to rank 1 on AT.
Definetly Unholy with shadow priest, they have high synergy (in 2v2 at least). It's top 5 viable setup (even on molten with bis geared pal wars, thanks to insane shadow priest damage).
Quick pro's + cons list;
[Unholy]
+ Synergy with casters (+13% damage, can afford to frequently grip offensively)
+ High survivablity, vs both casters and melees
+ Self sustainibility. You can stay alive quite long with death strikes, kiting, lichborne + self coils and just bandage
+ Passive CC with Desecrate.
- 3 min cooldown on gargoyle, needs heavy hitter for team mate in 3s usually.
- Overall low burst capability (CE limited to spawning pet every 30 seconds, Death and Decay** is 15 sec cd
** Death and Decay is not very high burst but should be used as part of it, it can quickly outdps Scourge Strike, can be precasted and doesn't require range
[Frost]
+ High burst potential with Frost Strike dumps
+ Extremely easy wins vs teams that trinket Hungering Cold at the same instead of rotating cooldowns...
+ Easy as 123, easy as Retri. Chains of Ice + Frost Strike + Plague strike with occasional obliterate...
+ 10 second aoe CC every 1 min, combined with Grip provides easiest gamebreaking CC ingame
- Melee range required explicitly to deal damage.
-Mobility can be issue, especially without paladin giving you Freedom or your team mate keeping things in range.
- Low survivablity vs casters (can be fixed by playing at pillar when your AMS etc is on cooldown.)
- Spam dispel on Frost Fever can be issue. (Having to spam mouseover icy touch/death coil on cleansing totem gets old). Not really issue during Hungering Colds.
- Burst can be prevented with Disarm effect
There's naturally more stuff but I think these are key points to both specs.