The basic irony of this thread never ceases to amuse me. So much hand-wringing over whether Jack or Tiger is the GOAT; the essential reality is that, in golfing terms, they are the same guy. If they weren't, we'd also be asking ourselves whether Faldo, or Seve, or Snead, or Hagen, or Vardon, or Hogan, or whomever wasn't also, perhaps, the Greatest of All Time. In some respects, all of the aforementioned were, too...but for the fact:
"Greatest of All Time" doesn't exist. Every man exists only in the time that he is given; for professional sportsmen, in sporting terms, that time ain't long. Jack: the superstar of the 1960s and 1970s; Tiger: the superstar of the 1990s and 2000s.
Why are Tiger and Jack so important?
1./ In a game dominated, in geographical terms, by the USA, they are both Americans; both of whom competed at their sport within living memory.
2./ They are quintessentially American sportsmen - they are to golf as Joe Namath was to football, Joe DiMaggio was to baseball, or Michael Jordan was to basketball. That's why American youths pestered their parents for a MacGregor persimmon driver on account of Jack, or a Nike titanium-balloon-on-a-stick thanks to Tiger - and then went to the driving range or golf course. Tiger & Jack "moved the needle, " (much as I hate that phrase). Are American sports-obsessed kids ready to get that fixated about a meticulous German or curly-haired Northern Irishman who blows hot and cold?
3./ They are both charismatic and looked the part at the peak of their powers. Jack the Golden Bear, Tiger immaculate in his red-and-black Sunday best - in a sport that has seen some truly horrible images [the kids aren't going to look at Daly or Poulter and think, "Now, where do I buy those pants?"]
4./.They won - a lot more than anyone else during their respective eras - [see 1./ (above)].
In other words, they're both great. Comparison is largely meaningless.