I think that this thread shows that there is no perfect group. Here are some thoughts especially considering all toons will be boxed.
Monk is best for hard pulls.
Tank - Warrior is best when boxing since he does not have to spam spells for aggro.
Slower - I would go Enchanter for added benefit of CC and buffs
Healer - I lean toward Druid but any will work as long as he does not box with the tank. (Shaman endless manna, and sweet buffs, Dru has DS and utility (DS, regen, gimpy rez, evac, ok buffs), Cleric has great buff and best heals)
Wizard - best DPS, but a Rogue can be used too
Last spot could go to a number of classes. Necro and bard would be high on the list. Mages are pretty nice too (if using a cleric maybe lean mage for reagents/dps).
Pairings should focus on the initial pull with Tag/Slow/Heal occuring nearly simultaneous as well as the "oh shit" situations. Players would be on the tank, healer and chanter initially upon tag. Switch to the other toons as they can.
Tank/last spot
Healer/Monk
Chanter/Wizard
Having said that, SK is pretty nice for tank/pull combo
Shaman are nice for the slows/heals combo, but it is hard to slow if you have to spam heals until it is slowed
Bards and necros add a lot of verstility
BST are pretty handy with Wizards.
There are a lot of really good combinations that will work really good.