HxH is vastly superior in near enough every category.
Plot-wise, HxH has good variety in it's story structure and theme exploration, whilst maintaining twists fairly unique to the Shonen formula. It may have had two terrible arcs (Greed Island and Election), but it's two good arcs (Yorknew and Chimera Ant) made up for it by being two of the best arcs in Shonen despite some minor flaws such as Emperor Time's broken nature or the Rose Bomb asspull, plus, I wouldn't say either of those arcs were quite as bad as Fishman Island. One Piece did have two fairly good arcs, though neither broke the mould or went into major depth with their theme exploration and the series as a whole has a very predictable structure with some very large contrivances such as friendship resolve boosts and a ridiculous amount of plot armour.
Bringing world building into this, whilst often praised as OP's strongest point, I'd say HxH does better than it here too. For one, Nen is a vastly better power system than that of OP's by making it far easier to not have the series ruined by power creep. Whilst OP had a fair level of that with it's Devil Fruits, the interesting counters they could give each other became redundant when Haki became a major factor in battles and even made some powerful DFs meaningless when the user lacked the Haki to back it up. The history of OP is indeed good and probably more explored than HxH thus far, though it's still lacking in the fact that most of it revolves around mystery boxes for key details that may very well be disappointing. As far as it's exploration of the world in it's present state such as the political and social state of it's world, I'd say this is a more even playing field. I'd still probably say HxH performs this better due to the detail in this area shown within the Chimera Ant Arc.
As for the minor aspect of pacing, I'd say HxH still holds the edge. Whilst Chimera Ant was slow paced, the same can be said of many of OP's arcs such as Skypiea and Dressrosa, plus HxH's average arc's pacing is still better for it's previous arcs. Also, pacing is nowhere near as important as writing quality.
Character-wise, once again HxH does many times better. The large majority of the main cast have great development, somewhat realistic/relateable in nature for the most part and distinctive in their nature, plus even the side characters are developed well and play good roles in the story. Whilst some of OP's side characters are developed well, the same can't be said for it's main cast regressing any development they made by the end of each arc, becoming fairly one-note in personalities the more the series goes on and not learning from their mistakes for the most part. It also help how the majority of battles are decided by using superior force to defeat the more intelligent villain as though intelligence is a crime, compared to the far more engaging tactical approach HxH takes with it's battle relying on some level of psychology and analytical skill. It doesn't help that OP has far more irrelevant minor characters that share similar personalities/roles and aren't given some sort of catharsis to remove their redundant role from the plot.
Art really depends whether or not we're talking about the anime or the manga. Manga-wise, there's no question this is where OP is leagues better seeing as how Togashi's average is lacking in detail and his worst is scribbles. Anime-wise, that Madhouse budget makes things the exact opposite.
So, overall, HxH does a lot better than OP, which will likely remain so with how Part 2 of OP has been thus far.
FMA and Ashita no Joe are far better Shonen than either though.
's One Piece.
aesthetically due to the intolerable text walls. If not for that and looking purely at it's writing quality, it still wouldn't be anything too good but wouldn't be outright bad overall (still better than any Part 2 OP Arc, at least).
