well i wasn't really a comic/anime person to begin with, the only two anime's that a followed when i was a kid were DBZ and YuYu Hakusho. other manga's didn't interest me at all. the first time i saw Naruto i thought it was rubbish, and didn't watch it again until a year later when they were showing marathon's of it on Cartoon network. i watched like 20 episodes back after back that day and really got into, i loved the concept of chakra, jutsu's, different ranks of ninja's and just the whole concepts of the series. after that naruto became a apart of me like an harm, i followed it ever since.
i had a similar experience with OP only this time i watched 20 episodes and still thought it was rubbish, the whole pirates concept was silly to me, the drawing was horrific, the fights was too straight forward. then i stop watching it and didn't watch again until just the other day (like 4 years later), i watched like 40 more episode it really got interesting no doubt a very good series, its better than Naruto manga wise being it covers more real life issue's such as slavery and so forth. but it was just not for me, i prefer the ninja concept more, chakra, jutsu's and etc. in my opinion naruto is more mature than OP not saying that OP is childish either. i like the whole layout, i like how the fights are unpredictable, every move is justified, every character has his or her limit. the moves in OP sometimes look so cheesy.
so yeah OP is better manga wise, but i prefer Naruto more, just a preference.