Apparently, you want to know the difference between the Blister backs (the ones with a cardboard backing) and the regular plastic bag wrapping. I don't think there's much of a price difference, collector wise (the blister packs come with three pez rolls instead of two, like the wrapped ones).
I am an avid PEZ collector and have two of each character (newer ones are repainted, or have different heads, Kermit and Piggy have new heads, while Fozzie and Gonzo are slightly different and repainted). They are my favorites along with my Star WArs and Simpson collections, and my Scrooge McDuck (still in packaging). I jsut wish they had new Muppet characters, though!