On one hand, it's frustrating to go through Victory Road in most games when I have a full party because one or two have to be HM slaves, so I need to keep depositing and withdrawing some members of my battle team so no one gets left behind. I've always been a fan of replacing them with key items.
On the other hand, I'm a big fan of Surf and Waterfall, and I don't want to see them go. Maybe have them be TMs?