This round's been a challenging one.
Dallas and
Dynasty had some great villains but delved into pantomime after a while.
Knots and
The Colbys consistently had better defined characters, so most characters whose behaviour at times could be seen as villainous (Knots's Jill, Joshua or Abby. The Colbys' Sable, Jason and Frankie) aren't really villains in my eyes because those actions are part of a more complex picture.
In the end, I've based my list on characters' actions in their first couple of seasons and the impact it had on those around them.
1. Blake Carrington
Dynasty
Ruthless businessman; tyrannical ruler of his servants and family; rapist; homophobe; murderer. Original recipe Blake is perhaps the darkest soap character of all.
2. Claudia Whittaker
Knots Landing
Whose control, deceit and manipulation was of Shakespearean proportions. Even understanding her motives, her cold ruthlessness meant that when cornered she could villain with the best of them. Lying to her daughter's face while purposefully destroying her dream of a scholarship; stealing a liver out from under a dying recipient (she had her reasons, but still... cold, cold, cold); framing her son to get him imprisoned - leading to his death; suggesting to her dinner guest she'd poisoned his food (and contentedly nibbling her salad while listening to him throw up said food), her villainy was a delight.
3. JR Ewing
Dallas
THE original. Accept no imitations.
4. Chip Roberts
Knots Landing
Soap's charmer... for as long as you're useful to him. After that all bets are off.
5. Alexis Carrington Colby etc
Dynasty
Perjurer; liar; stirrer; baby killer. And that's just her first half dozen episodes.
And a special mention for...
Danny Waleska
Knots Landing
As low as a snake's belly and proud of it.