What is the best proffesion for a DK?

[:1]I've heard that mining and blacksmithing is the best combination, but I'm not quite sure if that is the best combination. Any help?
Best for what, exactly? PvP? PvE DPS? Tanking?
DPs
LW/JC
Eng/BS
everything else
and do you have other toons with supporting profs or is your dk the only toon on the server