Update:
This http://db.vanillagaming.org/?talent#Iq0wAMboVo0b works perfect for me. I have imp on passive and phased, I drain its mana with Dark Pact and drain tank the mobs. I never ever stop for anything. One should keep in mind that full imp's mana bar or full player's HP bar is a waste. It is a lost opportunity for more mana with lifetap/dark pact. Fighting humans is a nice bonus if you are undead since you can cannibalize! It works perfect for any mobs of course.
Fighting 2+ mobs is even better