Who is better is just what an indivdual thinks. If I had to say who I prefer I would probabaly say Luffy not to sat I don't like naruto far from it.
In terms of fighting though hmm I have only seen till the end of the Alabasta arc so I can not even try to analayse Luffy's strength that he is currently in the manga.
Anyway if they ever met they would obviously become friends.