First starters, honestly, I hate the term "slave" (to rude and insulting in my opinion) I call them "HM Partners" or "HM Companions".
I only use 4 HM's - 2 a lot (Cut and Surf - two other are Fly and Strenght)
• Soul Silver I have not yet decided.
• Pearl, I have not yet decided on cut, Buizel is my main water Pokemon, and surf is one of my favorite water attacks, not just for HM, also a regular move.
for my Unova games
• Cut: my Liepard - its always part of the team
• Fly: Unfezant - usually in the PC
• Strenght: a Mienfoo - not the one I use in my team, but one in the PC
• Surf: Dewott - not just HM, I keep as a regular move too
other HM's I don't use, unless I really need them, I"ll search whom ever I have in the PC and is compatible with the HM.