i'm ignoring competitve eating because i find it obscene... anyways, moving on to the golf vs. tennis debate:
Tennis
tennis requires insane endurance and even a slight injury can be enough to knock someone off their game. as you get older, endurance goes down, # of injuries goes up. this extremely tough preqrequisite of physical conditioning is why no one can dominate tennis for very long. obviously, experience and skill count, but ultimately, someone younger will knock the champ off.
moreover, tennis is played against other people. those of you who think adjusting to a different golf course or the weather is tougher than adjusting to another human being's style of play either:
a) have never played tennis
and/or
b) are so athletically inept that playing against you might actually make that true.
Golf
golf can be played by 85 year olds, and the only physically strenuous act is driving the ball. however, 18 drives per golf game can't even come close to the number of shots a tennis player makes per game/set/match. unlike tennis, anyone at almost any age can be good at golf, so having one person dominating for a long time is more unusual, but it does happen.
golf is almost entirely a mental game: it's just you versus the course. obviously, knowing there's a good player going up against you will play a significant role on your psyche, but the actual physical act of making a shot has NOTHING to do with the opponent. you can play the course a thousand times to practice and, unlike a person, the course doesn't change its strategy.
Conclusion
so who is the most dominant? the key is that in tennis, you are really playing against other people. these opponents change their strategy and younger opponents can always show up with better conditioning.
in golf, it's just you against the course. if you can focus and drown your opponents out, you can dominate, as tiger has. in fact, they had to change the golf courses BECAUSE it was too easy to dominate the sport.
my vote is for federer. in a sport where every game is different, almost no one can even come close to touching him. at his current pace, assuming he stays healthy (which is far less likely in tennis than golf), he will shatter the records and go down as the most dominant tennis player ever.