Which one? Personally I like Silent Night,Deadly Night's Santa.
I also liked Larry Drake as the killer Santa in the 1989 Tales from the Crypt episode And All Through the House.
Here's my list of fav horror villains
Micheal Myers (from 1,2,6)
Jason Voorhees (F13 2 thru 7)
Cropsy (the Burning)
Freddy Kreuger (ANOES 1,2,3)
The most disturbing villains
Jack Torrence (the Shining)
Henry (Henry:Portrait of a Serial killer)
Frank Zito (Maniac)
Angela (Sleepaway Camp)
fav Classic monsters
Phantom of the Opera
the Wolf Man
The inbred,weirdo,mountainmen type killers in Hell Night, Just Before Dawn & Wrong Turn are very imposing as well.
I also like some of Leatherface's family members throughout the TCM series
the Hitchhiker,the Cook,Grandpa,Cho-Top,Tex,Alfredo & Tinker
There are so many others..I'll just leave it at that and let someone else fill in the blanks.