Astronauts. For one thing, their space suits would probably scare the Cavemen witless, and they may end up running away right off the bat. And even if they stick around, a lot of Astronauts are ex-military (Neil Armstrong, for instance, was in the Navy and served in the Korean War), so they're trained in hand-to-hand. Cavemen may be stronger, but that's the only advantage they'd have. So a hand-to-hand fight isn't a foregone conclusion in favor of the Cavemen. Nevermind the fact that Astronauts aren't the scrawny wimps some of you folks think they are. The guys that work at mission control are brainy wimps, sure, but Astronauts are typically in prime physical condition, so the Astronauts in this fight would all be in great shape.
On top of which, the Astronauts are MUCH smarter. While the Cavemen are trying to chase them around and beat them with their clubs, the Astronauts, if they decide to forego a physical confrontation, will be doing all sorts of sneaky stuff like setting traps and building a gun from scratch, like how Captain Kird did in the episode "Arena". 😀 If worst comes to worst, the Astronauts can simply rub two sticks together to start a fire (something which the Cavemen probably haven't figured out, yet), and then beat the Cavemen over the head with lit torches.