It depends what they are equipped with. A minotaur typically uses an axe, while a centaur uses double swords or archery. But since its a gladitorial battle, lets assume they have no weapons. The minotaur wold have a natural weapon with his horns, and powerful legs. read more
Beowulf is almost certainly superhuman. Grendel has far better killing feats than the Minotaur (killing soldiers with ease is better than killing virgins). Furthermore, Grendel has a charm giving him immunity to weapons. Beowulf was able to rip his arm off, but Beowulf is stronger than Theseus. read more
Of course, there’s only one minotaur, and canonically, it’s already been slain by Theseus, who actually did manage to overpower it rather than outwitting it. He had a sword. read more
The centaur seems to be ahead in the straw poling, but perhaps Brian Posehn is right: When a minotaur and a centaur fight, we all win. read more