I like the unholy build, but have not taken a death knight far.

www.talentchic.com is a decent site.
It will list the most common specs (via armory scans) for each tree.
You can check for pvp, pve, raids etc.
You can also check based on where your gear is from.
They have the most popular glyphs and enchants as well.

Not claiming the popular choice is the strongest, but when a lot of people spec one way, its probably not a horrid choice either.