In my personal experience, Shippuden was a drag... mostly. The only four (?) arcs I genuinely liked were the Gaara rescue mission, Team 10/7 vs. Hidan/Kakuzu, Jiraya vs. Pain (the best arc of the series, IMO) and Sasuke vs. Itachi (I don't remember if it's 3 or 4 arcs and I don't remember their names). Looking back at it, even Pain vs. Konoha was somewhat silly ("Talk no Jutsu" saves the day). The rest was a pain in the ass.
One Piece has MUCH better worldbuilding (Naruto pales in this area), better characters (most of Naruto's shinobis get the cold shoulder after Sasuke rescue arc, some basically just turn into cheerleaders, even protagonists... and, not less important, no character development outside of a few exceptions), better consistency (post-skip kinda messes it up for OP, but Naruto is inconsistent as hell), etc. The only thing that Naruto has going for it is, IMO, the pacing (which isn't great by any means, One Piece is just awful). The fights were better until a certain point, then power creep screwed over.
If we'll compare One Piece and Naruto, we should compare Pain's invasion to Enies Lobby, as both are at the same chapter range. IMO, Enies Lobby wipes the floor with Pain vs. Konoha, although Lucci is a simple villain in a character standpoint. Since you mentioned it, even Dressrosa is better (btw, I prefer pre-skip and Dressrosa is the best "long" arc of post-skip, IMO) and DoFlamingo is a better written character than Pain in my view. If we count all the arcs so far, none of One Piece's arcs were uninteresting for me, contrary to Naruto.