I'd be unorignal and say that my Bibarel (Rock Smash, Strength, Rock Climb, Cut) is my HM Slave, but to be fair, I also used a shiny Golem (with the exact same moveset, but replace Cut with Rock Blast, lol) when I got to the middle of the main story of Platinum. I used a random Starly for Fly and Defog, though.