I'am not 100% sure but I say Ash. Ash has like 60+ Pokemon so once the battle starts hes going to be overwhelmed pretty quick. If he summons summons Chief Toad or unleashes his fox power the odds are going to turn in his favor but in the long run I'am not sure thats going to be much help if Naruto gets worn out. Plus alot of Ashs Pokemon are faster.
ok wait, WHAT do u count as ash's pokemon. i mean if hes getting pokemon like lugia/unknown/ho ho/celebi/mew two etc then its MAJOR spite against naruto. heck i doubt even the kyuubi wud be able to survive an onslaught from multiple enemeis like that. on the other hand, if just has his normal type like pikachu etc, then he loses very very quickly.