I don't know. First of all FO3 is among my 10 favourite games of all time so it's not easy for a game to beat it IMO
Second I don't think these can be compared because although they share a post apolyptic setting and FPS gameplay, FO3 is an RPG, unlike Rage.
I'm sure RAGE's shooter gameplay will be largely superior, same with graphics, animations etc...storywise I have no idea. HOWEVER I doubt it will be better as a whole package, I mean FO3 is a game you can play wll over +100, 500 even 1000 hours; while Rage will probably last for a good while but nowhere near as long :shrug: Still I'm really excited for Rage, and is one of my most antipated games this year.