Floyd would probably make my top five as well, as would Sam, Crazy Harry, Lew Zealand... not really sure who that fifth would be. Nigel the band conductor, to complete Sex & Violence trio.
I mean, it's subjective; type in "Muppet characters" on Google and half the images are of Beaker.
To get off-topic, Nigel is one of the more interesting Muppet characters: you go from potentially being the host of TMS to being a really obscure background character; the fact he was also a Jim character adds fuel to the fire... give me that fanfic pls: Nigel with a switchblade behind his back approaching Kermit in a dark alley... they should've used him instead of Constantine.