I think a lot of the badges are cool, but here are my favorites:
-The Author: Because it makes you write better (or at least longer) logs and I really like this so the cache owner gets more feedback for the work he/she has done.
- The Brainiac: Because I am a fan of mystery caches, espacially the D5s are interesting
- The Rugged Cacher: And of course the other extreme, T5, is also exciting.