I haven't played golf, consistently, in the last 15 years. But I've always followed golf and remember watching and following it since the mid-80's.
I'm kind of a stats geek (background is baseball) and, at least right now, Tiger is the clear winner. He might falter, he might get injured, his play might drop off...but by any quantifiable measurement, he's way above Nicklaus at the same age.
I haven't read through this whole thread, but I'm sure at least a minority contingent claims Tiger doesn't have the same competition as Jack. To me, that's a fallacy based on results. In other words, because Jack frequently had Arnie or Watson or whomever in the hunt, you're assuming there were more golfers of elite skill level back then. Whereas I think it's more that the competition level is the same or better, but Tiger is an order of magnitude better than that.
Bottom line: Jack might steal a major or two from Tiger, all things being equal. But head to head in the last round of a major? Tiger wins two out of three.
Although, if you ask me who is the most purely
talented
golfer of all time--sans equipment, training, etc.--Nicklaus might be the one. It's like Deep Blue vs. Kasparov.