Mmmhhh... I don't think I can give a clear ranking yet:
York shin arc was really good, that arc was probably what really hooked me up to this manga. It is full of memorable moments.
Greed island. For sure one of the arcs I like the most, maybe even the one I like the most, I liked the training stuff, the card system mechanics, how clever everything was (nasty mortal combos with card powers and/or nen which resulted in bloody messes but at the same time really smart plans). And also having Hisoka as an ally was really funny and great (beside the oedo moment), Biscuit was good too and great as a teacher.
Chimera ant arc. I think this is recognized by most if not all fans as the best arc, it is the Marineford of HxH, one of the best arcs in manga. Really good.
The election arc was not bad too but at least a step below the others above in my heart.
The current Moby dick arc, or whatever it is called, is a bit weird to me, maybe too much stuff at once plus hiatus x hiatus don't make it really enjoyable for me.
The heavenly arena arc seems like a short arc, not much happens beside them learning nen, some infos about nen system, bullying a bit the handicapped wannabe bullies and a not so memorable fight with Hisoka.
The hunter exam was quite interesting but I don't recall many hugh moments: Hisoka is dangerous, some fights at the end and some other moments but it didn't really get me.
Same for the rescue Killua arc, I remember that training stuff with heavy weights, the sinister doggo, some scary moments with the coin plays by Goto and that is it.