Who is hotter Altair or Ezio

They are the same Model with the same face slightly altered from the original. The person they are modeled from is Francisco Randez. So there is no actual way to tell really. Though, you could compare their personalities and behaviour for example their experiences with and behaviour around women.
Altair so far has slept with one woman at an age clearly over 25, though is apparently very fertile judging from the fact he had several children (but still not that good with the ladies).
Whereas, Ezio spent his youth and most of his time (even when plotting revenge against the men who killed his family) working his way through every woman revealed in the storyline. The few who he encounters and has not had relationships with are his family (sister and mother) women over the age of 30 and Lucrezia Borgia who may have had several STIs which in turn may have influenced his actions.