I think Tiger is the best. But that's if you look at it at this point in their careers. Tiger still has a ways to go and a pace to maintain to keep that title in my eyes.
Jack certainly had tougher competition, and it's provable anytime you want to look at the details. All the Tour's "deeper field" nonsense (totally pumped by virtually all announcers, players, etc.) is self-interest, since it would be directly against their interests and potentially harmful to profits if they admitted that the competition of any other era were better.
The truth is, the "deep fields" of today simply don't matter. Take a look at the guys making between $600K and $800K around the #125 spot. Does it really matter to the legacy of a best-of-generation player like Woods how many guys like this were in the field? What matters is what the top competition is like, not how deep the money goes to provide a living for players who rarely, if ever, even sniff a win. And if you want to take Woods' top four competitors against the top four during any part of Nicklaus's prime, or the top five when Hogan was at the top with Snead, bring your money and let's have them play. I've got Palmer, Player, Trevino, and Casper (check the record before you laugh). Today, you'd have Scott, Stenson, Rose, and Mickelson. In 2003, you'd have had Singh, Els, Love, and Furyk. Fine players, all of them, and I'm a big fan. But against Jack's top four, in a seven-match series? On a course where hitting fairways and greens actually matters? Really?
Also: Look at Woods' record regarding how many times he's won playoffs with pars, or how many times everybody else around the lead completely collapsed during final rounds, leaving him to shoot 70 or 71 to win easily. His well-known record as a frontrunner, and his equally well-known record as a chaser (as in, he hardly ever wins a major when he's behind going into the final round), is a refelection of just how exceedingly rare it is that anybody else put up a credible challenge to him in the final round of a major. Idiot announcers often cite the "frontrunner" part of that to pump his image, but the truth is that it's just as much a measure of how his competition just isn't up to the level of what Jack had to face at every major.