I'm currently botting 3 DK's. All going blood with dual spec frost.
If using HB I use blood for survivabilitiy. Ya frost may kill faster.
But if ever get adds the blood will outlast the frost. Plus get the life tap heal. Combined with herbing, gives you 2 heals.
If using GB in area where mobs might kick my ass. I use blood. Macro with heals on 6 (I think)
If in area where I know he will be fine I use frost just for the pale horse mount speed buff.
Also if spec blood, with tank gear. And ever get bored wanna random. Instant queue as tank.
As for actual spec I used one from here on another thread. At work don't recall name. Use search. He has all specs linked. Mostly to eletist jerks.