I think the original Fallout PnP rules are good and solid. Also very good for new players who just played the CRPGs. It's a percentile system so its bonus/penalty modifiers is easy to apply.
Other than that it is really easy to die, easy to kill system (for humans, at least). And this is a real plus for a Fallout game, if you ask me.
Though the game actually have species other than human (deathclaw, super mutant, dog or robot to name a few), I never used those. Because they hinder the fallout-ish feeling of the game.
Aaand, also the sound of multiple dice (a lot) hitting the table while making a full automatic shot is awesome.