I don't think that there is a necessarily "WORSE" or "BAD" Muppet characters. They are just ones that are disliked by a number of people. I'm sure that you can find a reason to dislike Kermit or Miss Piggy the same as others can dislike Bean Bunny or Scooter. Personally, I like them all for different reasons, BUT some of them have to be in small doses or they really get either annoying or don't work. Like Pepe, he's not the most liked character, he gets annoying at times, but sometimes, he may have a line or 2 that would be kind of funny and he'll work in small doses. He may not be a good lead Muppet, or one that you can write a movie around, but he might be able to make a joke or 2 work. Just like Rizzo, once they started making him more of a sidekick to Gonzo, I think that relationship clicked and there was a reason to like Rizzo. I think that a lot of these "worst" on the list, and even on the list provided are a good example of characters that work by not being pushed a lot. Like Scooter, after a while the whole "Gee, my uncle wouldn't mind" and Kermit giving in thing got a little old, but he's still a good character. Wayne and Wanda were good as a running gag, and Janice is great at delivering the one line after everybody shuts up where she doesn't realize everybody stopped talking. Bunsen, when paired with Beaker, is a great example of "background comedy" where something funny in happening in the background and the guy in the foreground has no clue and just talking straight. The Bears weren't much of a "character" except one who was a security guard in Muppets From Space. The rest of the list would probably have been better in smaller doses(although I DO agree a little about Robin that he would have been better as a Sesame Street character, but he wasn't bad) but everybody has their opinion.
Daniel