Mew can learn everything!
Mew and Arceus learn every HM. Dragonite and Empoleon can learn most of them too.
Mew learns every TM. Arceus, Mewtwo and Gallade can learn most of them.
if you want a HM slave at the start of Dimond/pearl/platinum then bibarell can learn all HMs acept fly and defog, otherwise mew can learn EVERYTHING and all the legendaries can learn most of them.
Mew.It can learn everything and has similar stats to a blastoise.