I've been watched a good amount of the anime over the last year or so (at least, what's available with English subs). The juxtaposition of Kinnikuman's absolutely bumbling stupidity with how serious and stoic the rest of his fellow heroes are is what I always find to be truly the funniest comedy in the series. With that said, Terryman, Warsman, Ramenman, and Buffaloman in particular are the characters that put the biggest smiles on my face, especially when they get emotional and talk about their willingness to die for friendship. Warsman being a robot capable of crying just adds an extra layer of absurdity that's hard not to love.
BUT....if we're talking based exclusively on the figures... King Ton, Kinnikuman, PandaMan, Terryman with headband, Junkman, Ashuraman, Sawkillerman... Honestly, I could go on and on...