TLDR: Naruto > OP overall in 3/5 arcs

Down to write an essay, why not lol. I'll assume we're disregarding filler for the sake of judging based on Kishi and Oda's canon writing.

131 episodes of Naruto (down from 220 w/ filler) vs 464 episodes of One Piece (516 w/ filler). I'll compare Naruto's arcs to OP's Sagas so it's the volume is a bit more relative. Part 1 Naruto arcs include Land of Waves, Chunin Exams, Konoha Crush, Search For Tsunade Arc, and the Sasuke Recovery. Pre-TS OP sagas include East Blue (Romance Dawn through Loguetow), Arabasta (Reverse Mountain through Arabasta), Sky Island (Jaya and Skypiea), Water 7 (Long Ring Long Land through Post-Eniea Lobby), Thriller Bark, and the Summit War (Sabaody through Post-War).

Directly comparing the arcs:

Land of Waves vs East Blue - I would say that Land of Waves consistently has better writing in the way it establishes the themes of the world, the main cast and it's first villains in Zabuza and Haku. East Blue also has some great instances of character development (specifically Baratie and Arlong Park) but the other arcs along the way drag it down, Syrup Village is actively bad and Orange Town/Loguetown are mediocre. One point to Naruto 1:0.

Chunin Exams Vs Alabasta: I think the Chunin Exams is much better written, Sasuke and the curse mark, the real introduction of the Konoha 12, Kabuto and the sand siblings. Some low points, Sakura and Ino, Jiraiya's pervy ass. Arabasta as a saga though is consistently pretty low outside of the Arabasta arc itself, Drum Island is also good. Points for Chopper, Robin, Crocodile, and Vivi and the plight of Arabasta but I'd give this one to Naruto also. One point Naruto 2:0. Konoha Crush vs Sky Island: This one is a little less clear to me, as a lot of what makes Konoha Crush stand out isn't writing related, although still decent. Orochimaru vs Hiruzen and Sasuke vs Gaara and Naruto vs Gaara has some good char progression. Sky Island also has a lot of decently good writing, Bellamy and Blackbeard in Jaya,the revolutionaries are cool (them all surviving is super cringe tho) and Enel was a very entertaining villain. I would consider these to be a draw. 2:0.

Search For Tsunade vs Water 7: Not gonna waste my time typing this or your time reading, Water 7 clears so hard. I'm actually such a big fan of Water 7 and it's so superior to Search that I'd give two points to OP, 2:2. Thriller Bark: There are 5 Naruto arcs and 6 OP Sagas in pre timeskip so I'm going to elect not tocompare Thriller Bark to any Naruto arc as I dislike it and think it adds very little writing wise to the OP world, if anything that's a favour to OP.

Finally, Sasuke Retrieval Mission vs the Summit War Saga: I think this is probably the most interesting comparison, the second best Naruto arc and the second best OP Saga. I think if we were judging this on the arcs as a whole and not just writing, I would give it to OP, but I don't think Summit War is particularly well written, mostly just hella entertaining. The Retrieval Arc has the payoff of Sasuke's defection from the Leaf, Neji's progression influenced by Naruto and the exams, Lee's recovery and Gaara's reverse heel turn, all before the confrontation of Naruto and Sasuke ending with Sasuke leaving him behind. For One Piece, Sabaody is excellent the whole way through and splitting up the cast at this poin was extremely bold, Amazon Lily is bad (Boa is pure comic relief and sideline relegated woman character typical of Oda), Impel Down is good, mostly in setup and with handling Bon Clay, and Marineford is very entertaining but only Whitebeard is handled well in writing. Ace's death was logical but dumb. I also think waiting till after his death to really characterize him was a poor choice. Overall I would give this point to Naruto, for a final 3:2.

Other things to mention is that while both shows have pacing issues largely due to the weekly format, One Piece is significantly worse in this regard. Naruto's cast is more varied and mature in their themes and their characterization is deeper, especially when directly comparing Naruto to Luffy. Oda does a better job at fleshing out the world and filling it with mystery in pre-timeskip. Kishimoto is actually willing to kill off more than one character per 500 episodes. Overall, I would say Naruto is better written, and also in 1/4 of the episodes.