In One Piece (and manga in general) I prefer martial arts.
It looks better estaethically most of the time, you can actually see the impact of attacks and not just characters standing behind each other and sheathing their swords.
As far as good swordfighting in manga goes, Vagabond is at the top for sure.
Naruto had a couple of good scenes of sword or bladefighting. One Punch Man too. And Sakamoto Days has a couple of blade users but not so many blade vs blade fights.