I'm not that into the high 4 player end game scene atm but here's what I know

3x DPS builds (Generator Monk, Firebats WD, Archon Wizard)
2x Support builds (Monk Support, Barb support)

Generally people run 2x dps with one almost always being generator monk, one barb support and one monk support.

Lots of variations of course but this seems to be the top.