Unholy for everybody!

Why choose blood if you can AOE 10+ mobs everywhere as Unholy...

Level 60 looks like this:
http://imgur.com/a/zGeXn
At max level it looks like this:
https://imgur.com/a/o5njd

You will need (only) the following 2 glyphs:
http://wotlk.openwow.com/item=43672
http://wotlk.openwow.com/item=45804

Rotation looks like this:
Plague Strike, Icy Touch, Pestilence, Blood boil, Death Strike, Horn of Winter, Death Coil
Death Strike, Pestilence, Blood Boil, Death Strike, Death Coil, Death Coil
After the first 2 sets of runes continue to spam Pestilence, Blood Boil, Death Strike & Death Coil.
Later on you can use 2x Blood Boil at the 2nd set of runes and refresh diseases with Blood Tap + Pestilence when they are about to run out.

Happy grinding!

Yes unholy is sweet for AoE while you don't sacrifice anything on main target. And even greater if you focus on AoE.
I think using 3/3 Wandering plague, 5/5 impurity, 5/5 Desolation and Glyph of Disease would improve single target as well as AoE damage greatly.

DnD does more damage then anything else in AOE, plague, icy, pestilence, dnd - whatever by this time they are all pretty much dead anyways.