Basically the exact same deal for me. As long as you have a move that you didn't use a PP Up on that can be removed and replaced easily you're good.Gen 3: Zigzagoon (Cut, Rock Smash) and some random Water-type (Surf, Waterfall and Dive)
Gen 4: Bibarel - The lord of HM slaves.
The best thing about Gen 5 (aside from reusable TM's) is that you don't really need HM slaves.
Early in the game you need to use Cut a few times but you most likely don't have a team of 6 by then so you can just put a Patrat with Cut in there.
And because of the reusable TM's you can just teach one of your Pokemon Flash and Rock Smash in the instances were you need to by deleting a move you already have as a TM. So when your'e done you can just teach the Pokemon the TM again.
Another great thing about Gen5 is that you don't need any HM's (aside from Strength) to pass through Victory Road. It was very annoying in previous generations that you sometimes had to box one of your team members (if you had a team of 6, that is) to make room for a HM slave who knew, say Flash and Rock Smash.
This is a very interesting idea,Bibarel is, in most opinions, the best HM Slave. All it needs to learn is Fly and we've got ourselves the perfect slave.
I do wish that in the next Generation, Gamefreak would change the HM's to TM's and create Key Items that let you perform the tasks that HM's would allow you to normally do (like the "Floatation Device", which would allow you to surf).