Parar is more common, but that's rather because impedir means something different. While parar is of the flavour "something moves and then stops or is stopped", impedir is more "it's kept from even beginning". Impedir is more around the lines of "impede" or "hamper" than "stop".
Prevenir seems to be more common, but not by a huge margin. Also notice that prevenir can also mean "prepare", "warn", or "foresee", which makes it more context-dependent. Its general meaning is "to do something ahead of time" or "to come before (something happens)", "pre-venir".