I have no top 10 I can put in order.
So instead I'll just put them out this way...
Buffy "Anne" Summers
Xander Harris
Anya Jenkins
Spike aka William the Bloody
Liam, Angel (Angelus)
Cordelia Chase
Willow Rosenberg
Rupert Giles
Dawn Summers
Faith Lehane
The Judge (primarily for his aesthetics)
Android Moloch (see the Judge)
Mayor Richard Wilkins
The Master
Glory
Kennedy (she was hot, a hot lesbian so she had to be included)
Doyle
Tara Maclay
Daniel "Oz" Osborne
Wesley Wyndam-Pryce
Sweet (had great singing chops and was the big bad in arguably the best episode in the Whedonverse)
The Gentlemen (eerily scary and recognized as some of the most bad ass creeps in the Whedonverse)
Andrew
Jonathan
Clem
Captain Malcolm Reynolds
Jenny Calendar (so hot!)
Joyce Summers
Lindsey McDonald
Lilah Morgan
Lorne
Charles Gunn
Winifred Burkle (Illyria)
Jayne Cobb
River Tam
Darla
Kate Lockley (had her autograph sent to me from Fox studios), some people I knew on a personal level, knew her personally and used to go to college with her. In fact the wife of the couple that knew her, was good friends with Elisabeth Rohm. Unfortunately, she passed away. R.I.P. Aimee Redd.