Is it Mew(two) that can learn the most HMs or is it a different pokemon?
I'm just curious because I want an HM slave.
It is Mew, Arceus, and Sneargle, as they can learn all the HMs in any Game.
The Pokemon that can learn all HM's are Mew and Dragonite. Smeargle as well because it can Sketch all of them.
Source: http://pokemondb.net/black-white/hms (Check all the boxes on the top to find out)
Mew and Arceus can learn every HM.
Smeargle can Sketch them.