Overeem, by a mile. Look at Lesnar during the weigh-ins. Dog psychology. He knew he was nowhere near the alpha-male between those two and you could spread his stench of fear with a butter knife, it was so thick. This isn't a dig against Lesnar, because I think he disposes of 95% of the other heavyweights out there. I just think that when it came to Overeem, Brock lost because he knew he was fighting a bigger, stronger guy that can hit hard enough to KO a fucking rhino. Plus, Lesnar looked like a deer in headlights the moment he realized wrestling wasn't any longer an option. Then, Overeem just kicked him hard enough to make him shit his own asshole out. Ta-da.