Full team of warriors seems pretty impossible to beat if they know what they ae doing, so
that's my bet. They are just an unstoppable train of buffing, healing, stunning and windmill.

Full team of mages would actually be my second guess. I have been in near full parties of mages
and the perpetual stun and healing of all the mages combined is pretty cool.

Suprisingly I would put a full team of rogues last. Although they are pretty awesome killing
machines, they are also just a little to easy to kill without support. Unless they killed the whole
other team in the first few seconds they would all die.