Well, the pigs are probably the most obvious choice, so I'm excluding them 
My second favorite character is probably a rare amongst favorites, it's Ralph. He looks the best out of all of them in my opinion (mostly due to a lack of weird stuff like bent noses or Melissa's shirt), and I can't really explain why but I like his personality. I suppose it's because while he's not often directly funny, it's usually because of him that Bert's funny, but he doesn't have Bert's flaw of being annoying from time to time.