i think rasenshuriken is the better of the two justus. kirin has a limited use and requires a set up. once its set up it sure to be an instant kill, but if someone know about the technique before hand a counter is sure to be ready. even if you consider sasuke and naruto using there techniques head to head naruto would have a rasenshuriken ready before sasuke could meet all of the conditions. and supposing that he did, the naruto that would get blasted by kirin would most likely be a kagebunshin decoy.