TOS: Scotty (the miracle worker and the red shirt that never dies) TNG: Picard (the man is Regal, need I say more?) DS9: Quark (he is funny and someone was needed to lighten up DS9) VOY: Janeway (hard core decision maker) ENT: Porthos (who doesn't love dogs, but dogs in space - yea!)
Sticking with your TOS theme, Zephram Cochrane appeared in ENT "Broken Bow" and also in TOS "Metamorphosis"