I run with a lvl 27 Disc Priest, and x4 lvl 27 Demo Locks (imp corruption/imp life tap, 1 with imp Imp for Blood Pact, rest Imp Void)

I basically just dot/wand/heal. 3 Voidwalkers tank. Priest heals as needed.

I know they are early on, but they are MUCH slower than my PMMMM team, however WAY safer.

Personally I find the gameplay with my lock team much more engaging. With my mage team, I just jump in with Arcane Power and AE/Holy Nova till dead. My lock team feels like planned pulls. Dungeons do take a lot longer though, and if I'm just trying to grind, I'd go with the mage team.

Just my experience, hope this helps!