Honestly the way that WOTLK is currently, leveling up wise and the way that instances currently appear: I would strongly suggest you to roll something with a tank and healer.

You will also likely want something that gives the COE type debuff in a 3-5 magic user group, COE/Moonkin/DK.

Personally I would do:

Paladin
Moonkin (COE Effect)
Mage
Mage
Restoshaman (Bloodlust - also can lightning bolt ect)

for instances today.

For pvp, probably still 4 shamans/moonkin