Favorites:
Midna
Link
Kass
Ezlo
Beedle
Postman
Zelda
Tetra
Alfonzo
Least Favorite:
Navi
Dorephan
Zant
Linebeck
Malo
Not to say that I don't like some of the traits of the least favorites, but if I had to pick the least interesting characters it's pretty easily those.