I was going to say exactly the same as someone above, except the Destruction mirrors:

3 Sorceress, 1 Zealot

3 Sorcs will kill any player in 2 casts.
Zealots are the best ranged Healer, having no finicky mechanic to worry about. They don't need to be mobile, they can hang in the back with your Sorcs and heal. As a bonus, while controlling the healer, you can use his defensive target to heal other players on your team while your Sorcs assist and nuke your Offensive target. This will net you more XP and RP, and generally help your team out more. Healers make or break Scenario games.

I would avoid Shaman for Healers, as they utilize a busier playstyle to be effective, and also avoid Disciple of Khaine, as they make great HoT healers, they can't deal with spike damage unless you choose to melee with them as well, and this requires a lot of attention. DoK do get a group HoT thought, which would assist in easily managing AE damage. My advice is still sitting on a Zealot Healer.

The Sorc/BW, at Rank 10, get a LONG duration root, which has a fairly large radius. I really can't see any other 4 man team surviving the focus fire and round robin CC you would be capable of dishing out. The only issue would be the unnoticed or Stealthed Melee DPS, which have the ability to tear your zealot or a Sorc apart before you could do anything about it.

The mirror to Sorc/Zealot, as mentioned above, is Bright Wizar / Runepriest. Good luck.