Allow me to point something out? All FRAs on the comment that says "Meruem's only advantage is clairvoyance+teleportation (versatility)" will become invalid once I point this out.
Meruem's versatility isn't even a fraction of the real meaning of him being overpowered. It's not even the tip of the iceberg of what someone who looked at his character arc in Hunter X Hunter would see.
Meruem's biggest asset is his intellect, not any individual power, so something simple like "his versatility isn't enough" might be underestimating where Meruem's strength really lies, and how overwhelmed he might need to be in order to take free hits: both him and Netero during their fights were making perfect movements with flaws so insignificant that couldn't be called biases and yet Meruem would predict and heavily punish a mistake, analysing patterns to know when to expect it to happen and attacking with perfect timing.
Meruem is so ridiculously intelligent, so extremely good at foreseeing an opponent's movements and interacting with ridiculously complex and precise patterns where minuscule imprecisions cannot even be called biases in order to progressively corner opponents and force breaches in their defenses to open up for him to attack and severely punish them, he may as well just not get that one-shot he opens the potential for, due to simply punishing a flaw on Piccolo's moves and going back to full defense (or a dynamic of offense and defense necessary to block attacks and continue playing his game).
And that which I'm talking about comes from a fight against Netero, a man that was overwhelmed by Meruem's power, and yet managed to hold his own by being so skilled and intelligent that his flaws and imprecisions were barely significant at all and not humanly fathomable. Piccolo doesn't have that level of skill and is likely to get punished again and again without landing a hit, akin to a speedblitz, but intellect-based.
That would make this a similar battle to that between Composite Human and Baldi, wherein CH, a far weaker but far wiser fighter, defeated their extremely powerful opponent who could kill them off in a few blows, by using tools and tricks to overcome the difference in power and by using skill to minimize damage, deflect attacks instead of blocking them and such as to never really get that finishing blow, thus winning by the skin of their teeth.
So, now that nearly all the FRAs are dead, we have... two votes for Piccolo or so?
I am, of course, voting Meruem.
EDIT: Oh, just to add insult to injury, the very idea of an AP stomp against a Hunter X Hunter character with only the normal gap (five times) is already wrong. Not only is Piccolo's 97 megatons feat from his strongest attack while Meruem's 7-B would have his striking strength quite solidly scale from the Rose Bomb, but as a Nen user he can focus all or most of his aura in one part of the body to maximize offense or defense precisely there in detriment of the rest of the body. With his amazing foresight, there will be no possibility for Piccolo to exploit the weak spots, and this can increase his attack or defense for no less than two times no matter how you look at it, and that's not to mention the fact he can gather his aura over time or use charged attacks like a full power rage blast, while aiming for Piccolo's weak spots, to further help overcome the gap in strength. Of course, this is something most important HxH characters can do to some extent due to the sheer intelligence required to become a Hunter and how this level of intelligence is treated as fodder as the Greed Island arc comes by and hundreds of hunters are manipulated and tricked into their deaths before the ones responsible for that are outsmarted by the protagonist, deuteragonist and master.