What is the rarest silly band in the world?

Silly Bandz (sometimes called Silly Bands or Animal Bracelets) are mass-produced, and thus are not "rare" in the sense of collector's value. However, there are sets that are difficult to find, which could be considered rare.

There are a few packs of Silly Bandz that appear harder to find, such as the "Mickey & Friends Disney Bandz" and the "Guess Who Rubba Bandz," which are made to look like popular celebrities like Michael Jackson, Elvis and Sherlock Holmes. The "Hello Kitty Bandz" appear to be out of production, making them expensive finds on places like eBay. "Outer Space Silly Bandz" can only be purchased in the U.S. Space & Rocket Center, giving them high rarity.