My favorite Khan is Space Seed.
Me too. It wasn't a big action episode, but the dialog was smart and crisp, and I liked the Kirk and Khan scenes.
I know conflicts prevented Shatner and Montalban from ever being able to be at a shooting on the same day, but in my opinion, TWOK suffered from Kirk and Khan never meeting face to face. Most of their dialog was also simply Khan threatening Kirk and Kirk tweaking or taunting Khan.
Yeppers. Of the three, Space Seed is the superior production. You could have put a new villain into either of the movies and told the same story.
STID didn't need to make Harrison Khan. They had an interesting, engaging, villain that would have served the story as well, if not better. I think making Harrison Khan tied their hands to some of the story telling potentials they might have otherwise had.