The Best build IMO is SL. Don't forget it's all damage that's shared with your pet IE damage from Hellfire.

5 into corruption
8 to get imp VW
2 life tap
possibly 2 for suppression depending on how aggressive you want to play
Rest into Demo until you get SL then start taking destro.

The other important part is syncing you abilities properly. For instance...I have a bind that does Prayer of healing on the priest while it having a Hellfire channeling macro. At low levels you can do Rain of fire and say Holy Nova. I also have lifetap and Prayer of healing on a key. Two taps and the locks get a good chunk of mana and are healed for what they lost. If they're really low mana I just tap and hop or run around til mana is full then canabalise/bandage.

I think a lot of people forget or under estimate wands as well. Wands save a ton of mana and downtime and do more damage than say drain life even when specd in it until late game.