but as xhomerx10 said, the fastest average block confirmation time is the indicated value you should be looking for.
About the fastest transaction are like discussing about the priority, if someone pays more and they will get special access rather than the other are less for pay them. somehow I can say if the average timing of the transaction is same. more value and more priority.
True enough but that special access is consistent across all coins so the underlying indication of speed should still be the average block confirmation time. In saying that, I would imagine that most immature altcoins won't have a backlog of unconfirmed transactions so fees probably wouldn't be an issue in that case.