I personally would not go 4x Enhancement Shaman.

The 4x Elemental has a fair bit going for it.

Casters in mail with shields is very good protection vs melee.
Melee in mail without shields, is middle of the pack.

Elemental has massive controlled burst via Elemental Mastery, Flame Shock, Lava Burst.
Not sure that Enhancement has anything like this.

Either set has several totems, for assorted buffs.
Both sets have heroism, rez capability and self rez for wipe recovery.
Elemental is geared for spell power, which makes their heals far superior to Enhancement.

I'd personally go... Paladins, Death Knights or Feral Druids for a melee group.
Possibly a different class on the leader then the rest of the team.