I dont think the choice between Graf and Seles is easy on this one. For starters Graf won 8 of her slams before 1990, so only 14 in the 90s to Seles 9, not as big a difference. Secondly Seles won 9 of the first 13 held at the start of the 90s, until the tragic stabbing between the 93 Australian and 93 French Opens; Graf won only 3 of the 13 held during that duration. Of course Graf ended up winning so much more than Seles in her career, that even with all the what ifs, one cant change what happened, and Graf will be considered higher rated all time than Seles. However with the Grand Slam gap so much closer discounting Graf's 80 slams, and Seles dominating Graf for 2.25 years in the 90s with both clearly one top, something Graf only did for 1.25 years to Seles, the first 1.25 year in Seles comeback before Hingis took over, it is a tough call IMO. I still voted for Graf but it isnt clear cut, to me anyway.