A bar room brawl:
It is not the size of the size of the warrior/thief/Mage in the fight but the size Of the fight in the W/T/F
I have heard tell of a bar room brawl in France during the 100 years war between some mercenaries and more chivalrous warriors.
While the warriors rushed for their swords the more practically minded mercenaries beat them down with chairs or other handy blunt objects.
Mm.. I have to agree.
Consider the setting - a typical bar would be very busy, full with the working class. So it's quite a small room with far too many drunk bodies inside it. There are lanterns and candles for illumination, and the battle takes place in Skyrim. For whatever reason, the thief, warrior and mage have an argument that can only be settled when two of the others lies dead.
I'll start with the mage:
The mage only has the school of illusion at his fingertips. Because of the local attitude towards magic, he would be suicidal to use his magic, and so he instantly loses the school of destruction. The school of conjuration is also unavailable to him - summoning Daedra or raising undead would not be looked at kindly. Any spell he does cast must be very subtle, so as to kill the target without anybody else realising that he is using his magic, or else he won't leave the room alive (it's a crowded pub, so invisibility is useless.)
He could use frenzy to start a barfight and then slip off in the confusion, so long as no one realised his role, and he could use calm to prevent the fight ever happening. But the latter doesn't win him the fight. So his best bet is to start the bar fight and get out of there quick-smart.
The warrior - his heaviest weapons are unsuitable to fighting in a small room crowded with bodies that aren't interested in the fight. He probably has a knife on him and he can use his body mass besides that. However as soon as a fight starts the boozed up bar patrons are probably quite likely to join in with the fun, so that will get out of a hand quickly, and if he draws a weapon then it will be a free for all with everybody using daggers and improvised weapons. He likely doesn't have his armor on him, so he has less chance of survival than the thief (he's slower and less agile, and equally as protected without armor)
That only leaves the thief - who should be in his element in our barfight scenario. He should be able to use the crowd to his advantage, would be the most willing to fight dirtily and survive and is the one who is most likely to be able to use his knife in the confines of the bar without anybody noticing that it had happened until it was too late.
It's really anybody's game, but my preference lies with the thief. It's his environment after all.