IMO it was the late 90s to about mid 00s or so. there were still graf and hingis around early on and then we had the williams sisters, henin, clijsters, davenport, capriati, a past prime but still good seles (till early 00s). also some more good players like mauresmo and the armada of soviet players (sharapova...). after that tennis went downhill of course with very weak no. 1 players (safina, jankovic, ivanovic, woz...) but for that time I think womens tennis was really good. also womens tennis was financially booming back then and WTA players were huge media stars.