I love Egghead, but I gotta give Shame a headstart. Cliff really aced his second appearance and created what so few were able: an original villain with a memorable personality (He is basically George Bush as a supervillain).
Another aspect that made it fun is that unlike the rest, he is a leading man. Most villains were twisted and crooked rubbing hands, mustache twirling sort of way, Shame is an alpha dog like Batman, which makes the antagonism interesting.
Egghead is pure Vincent price syrup. He steals every scene and you can't help but love him for that. Tut steals and it's all about his drama; instead, Egghead makes it clever and fun without trying. However they relied too much on this in the third season. The best showmanship can hardly substitute for the lack of plot.
In many cases the actors were good, with great presence, take the Clock King or the Puzzler, but they were just not as magnetic as the Penguin, the Riddler, the Joker, Tut or Egghead, or as fun as Julie's Catwoman. I think David Wayne and specially Sanders went in the opposite direction. The Mad Hatter is an odd little gentleman and Mr. Freeze is all about his tragic situation. I have no clue why Otto was the most popular Mr. Freeze.