Depends on your class. If you can heal, you can get instant q's in dungeons so that for me is the fastest way. I wouldn't recommend anyone to tank using dungeonbuddy, but I am a rebble and usually will tank...
my favorite tanking instances are sunken temple and violet hold because there isn't any movement really.
tanking is dangerous too because it usually only pulls one mob group at a time, usually people don't like this.
Edit: didn't see you were blood dk... you could also do mixed mode, where you do something like dungeon and archaeology...
basically my experience to getting to 90 is I can do it in a day or so with dungeons and it takes 3 or more days questing. It really helps with heirloom gear and all the battle standards as well. There are plugins that throw down battle standards to help your bot. Unfortunately mixed mode doesn't support questing and dungeons, it just doesn't work if you try. It used to at least attempt to do it when trying, and it used to work for me, but now I think they made a check of some sort in the code where it just flat out doesn't work. If you try and doesn't work, the only response you will get is it's not supported.
