@Fergun: Vendetta isn't that bad for grinding only, but not really necessary if you use your diseases right
You are already 80 I presume? I don't know how good your gear is and what you want to farm, but most abilities aren't necessary until you hit ILvl 232 Gear. But ok there are your 4 speccs:
I would recommend a blood specc with unholy subspecc. Frost subspecc should be inferior to it cause you don't gain that much out of more magical dmg and autohit dmg. With blood, most of your dmg comes from abilities and not autohits.
If it's only grinding you want to do, I would use a different specc, but you can use the second. but please don't put 64 points in blood.. that's overkill and absolutely unnecessary.
The first specc is absolutely craptastic, you miss many main abilities like full death rune mastery, bloody strikes, sudden doom etc.
Third and fourth specc I already mentioned.. there is no reason to use a frost subspecc.
I would use this one:
Your Glyphs suck more or less, no need for DRW and Vampiric Blood Glyphs. Use the slots to push your overall dmg so you can kill the mobs faster. A nice idea would it be to switch e.g. the Runestrike Glyph against a Death Grip Glyph so you can chain grab the mobs. Way easier than running around
The last points you can use as you see fit.
-Take 1Pt Improved Blood Presence, 1Pt Vendetta or Vampiric Blood. If your Gear ist not that good use Vendetta to replenish a bit of your HP after each kill.
-The rest should be simple. For farming you don't really need Demonic Rune Weapon because your enemies won't last so long that you can use it. But there are not many alternatives. I would recommend going for 5Pt Blood Gorged and 2 Pt On A Pale Horse so you can move faster from one spot to another.
No real need for things like
-Epidemic: Your Enemies will be dead before your diseases will run out
-Runetap: Your Death Strike and Blood Worms will heal you enough
-Vampiric Blood: Are you hunting Worldbosses? I don't think so. If you are not in full blues and want to hunt elite mobs there is no need for that.
-Mark of Blood: Again no need taking it. Only a bit helpfull if you run into fast hitting mobs, but not that much. Will run out before the 20 charges are used.
-DRW: Mobs will be dead before its used. Use your Runepower for Deathcoils instead