Tiger is easily the most dominant with Federer a close second. In golf, you are playing everybody. All 125 or so guys who start on Thursday are on an even plane. However, even in Grand Slam tennis events, you have to win seven matches to get the title. Difficult no doubt, but usually the top seeds don't even get decent competition until the fourth round. Also, consider that Federer has arrived in a time where there is not a true rival. Nadal on clay, but that is all. Agassi, at 35 years of age, almost beat him at age 24 in the US Open finals last year. Agassi at 36 and with a gimp back beat the 8th ranked player in the world this year at the Open (Baghdatis). Do you really believe that if Federer played in the time of Agassi, Sampras, Becker, Courier, Edberg and the like he would have been as dominant...the answer is no. He still may have been the best; this is debateable, though. Tiger would have dominated any era. That is clear. Wariner, the sprinter, is the MJ of track and field; he is amazing. I would have loved to have seen him race against Michael Johnson.