I'd rather have Megaman than Ridley and Geno. I know everyone loves Geno, but he'd be a better assist trophy since he was only in 1 game. Megaman however has had MANY MANY games on the Nintendo systems and is much more famous really, since he is with Capcom.
And his moveset could be endless, he could be like a Kirby version of Samus and get people's abilities for his (X or M) Buster and kill everyone with their own elemental/physical abilities. Think about it.
*Megaman steals Ike's Fire powers, uses like... a fireball or something and kills Ike*
And Ridley is a boss, not really a major character that people play... ever. o.O
Metaknight is playable in alot of kirby games, same for Dedede. So they can't count as bosses. I'm sure in Wolf's case yet, but he was probally playable in some Starfox game.