Obvious bias aside....I think One Piece is an amazing manga. It has amazing quality in emotions, fighting, and humor. I don't think any other manga has made me laugh despite the arc being in a serious moment! And I don't think I've teared up as much with the character histories as I have with OP....I think it may even be the only manga where a Flashback is a welcomed thing...just because a good story will be comming!
Oh...and if you're new...watch the anime, and then when you catch up....haha after over 500 episodes....read the manga ^.^!
I would say you could almost watch the show and not even notice when some of the episodes were Filler....especially good fillers like the G-8 filler arc!