Doing either is pretty redundant at this point when Hunter X Hunter does everything it does better (and there were plenty of other Shonen before or after it the same can be said for). Still, if wanting to view it, then the form depends on your priorities. Manga goes into more detail on several events after the last main battle, but has terribly inconsistent art and the last few chapters are very anticlimactic. Anime has better art and a better ending, though does alter details on Mukuro's backstory (though the manga version was overly edgy) and has some slight powerscaling inconsistencies in the last arc. I'd say the anime is the better choice overall.
Super Saiyan said:
Is the art better than HXh?
Manga-wise, it's arguable. They have comparable peaks and both become fairly lazy at points, though YYH at least never reaches scribble territory.
Anime-wise, its art is better than 1999 HxH, but vastly inferior to the 2011 version.