One Piece is so much better than Naruto. It's funnier than Naruto, it has better character development than Naruto(However, Naruto's character development is good though, don't get me wrong.), it has better fight scenes than Naruto, and it's all around more enjoyable than Naruto. And pirates totally pwn ninjas.
I guess the thing I love so much about OP, the thing that makes it so entertaining is that I love it even though it's sort of a positive, happy-go-lucky story, where hardly any main character dies(instead they just get seriously fucked up). And my favoirte anime are mostly dark series like Hellsing, YuYu Hakusho, and Gungrave. But OP which is anything, but a dark series(well, it does have some dark parts, like the Arlong arc) is in the the top 5 in my favorite anime/manga. Even though it's an optimistic series, it's just so badass that I can't help but love it.
Plus, the way Oda develops the characters and their backstories is just excellent. Every character he creates, even the smaller ones are all brilliantly developed. Sanji's past and why he ever won't let someone starve was really great. And when they revealed why that guy in the Arlong arc with the pinwheel on his head(forgot his name) started wearing the pinwheel, I was sorta shocked since I thought Oda just put it there as a part of his wacky character designs.
I originally liked Naruto better at first, since when you first hear what each is about, Naruto does sound better and more badass, while One Piece sounds like some crappy kiddy pirate tale. Plus one of the first chapters I read from One Piece was from the terrible Buggy arc, so of course I originally liked Naruto better. But after reading the Kreig arc in OP, I said to myself, "Fuck Naruto! This shit's much better." And that's pretty much when I started to love OP.
IMO, Oda is a god of manga to be able to take a story about a rubber pirate and his crew looking for some legendary hidden treasure and make it into such a badass story with excellent characters and enjoyable fights. Naruto can't even compare to One Piece. It's a reat series, just not up to OP's level of greatness. Plus the Narutards are annoying as hell.