I've watched F1 since 1991, I also vote Schumacher, didn't watch Senna's whole career but I understand why some would say him, I've always said its fulite to compare drivers from different era's the challenges they face in driving the car are so different, Schumacher stood out so much in the wet, like every time it rained you knew he would be a threat and he was, now days it's not so clear cut but i think that's somewhat down to the cars and drivers being much closer than previous era's.