Peak Serena vs peak Seles
The Seles of 91-92 vs the Serena of 2002-2003 who wins. I would favor Serena on all but clay. Not sure who is the better player in that instance, probably Serena as most regard her playing level of 02-03 the highest ever by a women even if statistically both Serena of 02-03 and Seles of 91-92 are inferior to Navratilova of 83-84, Graf of 88-89, and some corpses from the distant past. However it is close in that sense. However as far as a head to head matchup Serena and any huge power player who also moves better than Seles is a nightmare matchup for her.