Tough to say at the moment, especially if it's Dragon Force Natsu vs Kyubi Naruto. About Naruto's recent speed increment, Bee said that all he sees was a yellow flash. Now, if you remember Jellal during the tower of Heaven, when he used Meteor, it was fast that Natsu barely could react. However, after Etherion, he easily caught up with Jellal... and still not at the full potential of Dragon Force. Then again, we haven't see Naruto's true strength with Kyubi's chakra, so it's still tough to debate.
Personally, I think Natsu would defeat Naruto by a very slim margin...