What are the best HM slaves for each generation, based on availability? I think you need two in all of them except maybe I so what are the two that cover all HMs that are available earliest?
Please note that Fly is a good move in single player and Surf is a good move period, so you don't really need slaves for them.
Tropius + Golduck cover everything, even the moves that aren't HMs in every game like Flash/Whirlpool/Defog
bidoof is the only true hm slave, others are just posers