HM Slaves.

Tropius is really good as it can learn Flash, Cut, Fly, Stength. Other HMs are all water type, so many water pokemons can do the job.

Well, fly is a pretty strong move that helps in battle, so I would keep that as a actual move, and you can also give one HM to each pokemon, so then they three good moves and you can also have all of the HMs except for Dive, but Dive isn't useful. And anyway, if something comes along that you want, just go to the Move Deleter.

Golduck can learn dive surf strenght and waterfall i think

The easiest way is to catch a swanna for surf and fly because that all you really need

the best hm slave ever is linoone: strength, surf, rock smash, cut not sure if it learns more or not

for the main game I just put the moves on what ever pokemon I had that could use what I needed there is always the move deleter and relearner heart scales are easy to come by and the moves you need are not horrible.
**spoiler**(post game info)
I use Tropious with
fly (first move so easy to get to)
flash (not an hm but useful)
Strength
Cut

I team it with Carracosta
Dig (if I can't fly will take me where I can)
Surf
Waterfall
Dive

you can catch Tropious on route 18 15% encounter rate
Carracosta is from the Cover Fossil when a fosil is offered to you in the relic castle

I think the ultimate HM slave is zigzagoon XDD can even learn surf and most of the HMs (except fly)O.o