I have seen a lot of them both. There are similarities in that each was the odds on favorite everytime they tee'd it up in a major. They both hit it so far in his day, and they both made every single putt that they had to make.
I'm going to say that Nicklaus had more great players to beat, Palmer, Trevino, Watson, Player, Casper, etc. Tiger has a deeper field each week.
Nicklaus won majors from 1963 til 1986. Set scoring records on a regular basis.
Tiger has done some things that just amaze me! '97 Masters, 2000 US Open, Grand Slam (4 in a row is a grand slam!). Then playing 91 holes with a shredded knee and stress fracture and winning the US Open last year!!
If he is able to come back from his injury and stay healthy, there is no reason to think that he won't win 25-30 majors and 100 tournaments.
Tiger might be the most incredible sports figure of all time!