Meh, I have to be honest. HxH is very overrated here, One Pieces far superior in almost any aspect.
-Plot:
OP. HxH don't have any plot XD
-Main characters:
OP. There's no debate bro. Togashi can't even give a role in the history to Gon and Leorio, and this last guy has a very pathetic development around the series. He is useless and didn't even has a nice characterization as medic, he onle tells his sad past and that's all. In One Piece only Nami's story stomps any MC of Togashi.
-Side characters:
OP. Side characters in HxH are just too boring, Togashi can't introduce a new mystery or character without make it being related to the DC. A mystery box.
-Villains:
OP. WG is the best villain in the nekketsu.
-Character designs:
OP. That's something more personal, but I like more Oda's character design. Togashi also had a shit drawing in this manga.
-Power system:
Tie. Nen is excelent to explain simple things (almost all the abilities of the characters are children games), but when he needs to explain something mor ecomplex he creates something VERY convenient (like Kurapika) or a shit like Gon's rage and Alluka existence. And I have to thing that this shit is good because "bruh, Dark Continent".
DF/Haki system is more simple, but works better.
-Story arcs:
OP. HxH only have 1 good arc.
-Incorporation of themes:
OP.
-Art:
OP. Oda have a most consistent work around all the series, a lot of imagination and, I have to say, a better drawing style. Let's be honest, Togashi's ego damaged a lof the manga.
-Imagery:
OP.
-Panelling:
OP.
Oda stoms, Togashi don't
have any chance. One Piece create some of the most iconic manga panels in the shonen, and I don't care how much the huntertards can defend Togashi's work... Is the worst in the nekketsus. I know about Togashi's back problems. But he don't wants to taking over the job from a well-qualified draftsman out of pride is his problem.
-Originality:
OP. How can you thing that HxH is more original than One Piece?
-World building:
OP. I don't have words to describe the ABYSMAL difference between the WD of this two mangas. One Piece is in a level TOTALLY DIFFERENT.
You can wath it for yourself. Let's be honest, Togahi's wolrd depends of a McGuffin or Mystery Box all the time.
-Characterization:
OP. HxH's cast characterization is no existent (as almost all the members of Phantom Troupe, Zoldyck Family or Zodiacs), inconsistent (Kurapika talked a lof of how the Hunters are "proud" and honorable people, but then he don't seems angry or outraged at how killers can get licensed and kill other hunters) or bad (Gon is the worst character). Of course, there are good characters with a great characterization like Kurapika (if I ignore the last thing), Meruem, Pitou, Hisoka or Netero, but almost all the cast has a very inconsistent characterization.
Oda usally works it better. Giving a rol to all the characters in one saga, and I he don't have something to do with them he sends these characters to the next island. I mean, every Mugiwara has his own saga, and enought screen time to have an own personality. Of course, some times Oda has to make more focus in other elements, but thanks to it we have some of the better characters: Oden, Edward Newgate, Garp, Doflamingo, Corazon, Law, the Nine Red Scabbards.
I mean, a lot of this work usually is forgotten for all the poeple. But is this focus in te storytelling that Oda can give to use some of the best lines in the series.
"I would enjoy the chance to show you my skill with the balde"
-Enjoyment:
OP if you want a great adventure with a lot of focus in the storytelling and a huge lore, HxH if you want overexposure and turn off your brain.