I would get the John Cleese from Sideshow (If he didn't look like Colm Meaney)
That reminds me, what scale should the guest stars be in? The 6 inch scale (like Lord of the Rings and most superheroes) are about the same height so they look in scale. However, the 12 inch (like Sideshow and let's face it, Barbie) tower over the Muppets but look like the could use the Muppet figures as actual puppets.
Granted, it's a silly waste of time thinking about it but what's your opinions?