Vince, quite easily. One's just a promoter, the other is a bonafide business man that literally changed the landscape of one industry. Dana is damn good at what he does and has done more for MMA than any other person. But Vince has made cultural icons out of Hogan, Andre, Rock and Austin. UFC fighters don't have that longevity. Chuck Lidell was on top of the world four years ago and now no one cares about the guy. Tito Ortiz was recognizable and now is washed up. Matt Hughes is done. UFC has too many variables for a fighter to become a mainstay cultural phenomenon. Wrestling has always been that, but Vince found a way to make his guys stick in peoples minds. Plus, the E runs 400 or so profitable shows in an industry that has been over exposed for over 20 years and the UFC runs what? 30 shows a year during their first boom period. Vince has longevity, and his product has spawned into movie production and has made national celebrities out of the Rock and Hogan. The E's global presence is larger too. Dana is just ridding a high right now and doesn't have 1/10th the business portfolio that Vince has.
From a non bias, purely objective standpoint, the only answer is Vince. He did it with his own money, stomped out all competition and has done it wayyyy longer than Dana and through three very different decades. More tv product, a 50,000+ crowd at least once a year, more merchandise sales, more DVD sales. It's not really debatable. One guy in a really small pond during a fad boom or a guy who changed the landcape amongst many, many competitors and differing regional tastes? From a business standpoint, Vince by a mile.