Post by Aleanos
Well since you're going for a "fresh start" I'd suggest you check out the stickies
before anything, this one
in perticular should you need a walkthrough on Dk's in general.
But since your question is about the talent trees I might aswell offer you my view on their differences :)
Blood is a tree that focuses mainly on Physical damage and self healing, this includes Big Juicy Critts and numerous ways to restore your health.
Unholy is a tree that mainly focuses on magical damage, empowered diseases (including a third one!) and a pet ghoul. (It has great aoe capabilities)
Frost is kindof a mixture of the two, it's a tree that focuses mainly on two abilities for damage, Frost strike (which deals frost damage based on your current weapon) and Obliterate (and physical strike based on your curent weapon. The Frost tree also has increased AoE capabilities thanks to Howling blast (and aoe frost "cone" almost).
Which build you pick really boils down to personal preference, but many people go for Blood at the start (due to the increased healing, giving you many "Oh snap!" for emergencies) or Unholy (for the increased aoe capabilities and 20% increased mount speed On a Pale horse
Also, going deep into one tree is suggested :)