I think that we all will never agree on whether one winner or team winners is better, but we don't need to. What we can all agree on is that it should be stated up fron if team winners will be allowed. Because if one person is playing on the assumption that there will be only one winner, and two people are playing with the assumption that they will be team winners, the single person is going to get stomped almost every time. It's not fair to simply say that "Well he should have got an ally then" because many people don't like playing that way. If you tell them up front there will be team winners they will probably pick another game. If you tell them up front that there will me only one winner the two people can still ally, but they will probably not cooperate quite as closely. They will only help the other guy as much as is neccesary to remove the other empires. Which gives the guy more or less going it alone a more level playing field.
So the moral is state the objectives up front and stick to it.
Geoschmo