My main HM slave is my Diamond starter, Empoleon. Its moves are all HMs. It is also my best Pokemon at level 100, can beat nearly all others, and can 1-hit KO most Pokemon with just one Surf. In my list,cIconly show HM slaves and their HM moves.
Empoleon: Surf, Rock Climb, Rock Smash, Cut
Staravia (lvl 22): Defog, Fly
Giratina (lvl 70): Strength
Mewtwo (lvl 75): Once knew strength
Typhlosion (lvl 100): Once knew strength
Celebi (cannot remeber level): Flash