Which singing villain has the best speaking and/or singing voice to you? I'll add any, whether I like them or not, but I'm only counting villains who have a musical number of their own.This isn't just for principal villains. This should also include secondary, supporting or minor villains as well. But this table only includes villains who sing. It doesn't count my opinion.

Villain Film or TV Series Speaking Voice Singing Voice
Ursula The Little Mermaid Pat Carroll Pat Carroll
Zira The Lion King II: Simba's Pride Suzanne Pleshette Suzanne Pleshette
Judge Claude Frollo The Hunchback of Notre Dame Tony Jay Tony Jay
Scar The Lion King Jeremy Irons

Jeremy Irons (mostly);

Jim Cummings (partially, after Irons' vocal cords were strained)

Si & Am Lady and the Tramp Peggy Lee Peggy Lee
Gaston Beauty and the Beast Richard White Richard White
Jafar Aladdin Jonathan Freeman Jonathan Freeman
Mother Gothel Tangled Donna Murphy Donna Murphy
Nuka The Lion King II: Simba's Pride Andy Dick Andy Dick
Vitani (young, that is) The Lion King II: Simba's Pride Lacey Chabert Crysta Macalush
Dr. Heinz Doofenshmirtz and his 2nd dimension counterpart Phineas and Ferb / Phineas and Ferb The Movie: Across the 2nd Dimension Dan Povenmire Dan Povenmire
Dr. Facilier The Princess and the Frog Keith David Keith David
LeFou Beauty and the Beast Jesse Corti Jesse Corti
Drizella Cinderella Rhoda Williams Rhoda Williams
Alameda Slim Home on the Range Randy Quaid Randy Quaid
Fat Cat Chip n' Dale: Rescue Rangers Jim Cummings Jim Cummings
Don Karnage Talespin Jim Cummings Jim Cummings
Marina Del Rey The Little Mermaid III: Ariel's Beginning Sally Field Sally Field
Captain Hook Peter Pan Hans Conried Hans Conried