Ag! So much!! But here goes...
The prettiests is... jeez, this is hard. But I think I'll have to go with Buffy. She has the perfect face and perfect hair and perfect everything. Of course, everyone is so good looking that it's really hard to choose. But I think Buffy is the most consistently pretty.
The smartest is either Willow or Fred. I think I'm going to have to go with Fred on this one.
The stupidest is Riley. All brawn, no brains.
The baddest is, assuming "baddest" means most sinister, I'm going to say those watcher guys from Get It Done who "created" the Slayer. They give me the heebie-jeebies.
The nicest is Clem. So welcoming and friendly to all.
The coolest is a three-way tie between Faith, Lilah, and Dark Willow. They're all so cool!!!!
The strongest physically? Glory in a heartbeat. Mentally and emotionally? The Buffster.
The weirdest is Clem. I love him so much, but he's big with the weird.
The most moral is Tara.
The sexiest is Faith.
The most consistent (as in the person who's arc was always character-consistent and very natural) is Willow. With the exception of that Wander incident in season 3. Seemed forced.
The sincerest (most sincere) is, of course, Spike. 🙂
The most amazingly wonderful ever (a creation of my own) is, of course, Willow.