Well....if we are going to talk about other murderers...I would have to mention that guy from Etude in Black!!

Oscar Werner in Playback. More machine than human.

Robert Culp in Double Exposure. So darn efficient and cool and smart.

James Read in Uneasy Lies the Crown. He just giggles at Columbo. A slacker who has never done any work in his life except for sponging off of someone. One of the true all time heels in the series.

Ruth Gordon. Abby not only murders her repulsive nephew to achieve justice, she disgraces him by making look like he was going steal from her. That poor little old lady. Most original murder weapon ever.

yes cassas...i would have to say the second runner up would have to be john cassavetes!!!! oh my god, he was so gorgeous!!!! he couldve killed me anytime!!!!

i tend to like cassidy the best as a killer..hes smooth, suave, snotty as hell and you enjoy watching him squirm!!!! He does it so well and i love his sarcastic sense of humor...

sabra..........you are my newest best friend!!!!!! jc was beyond sexy............what a freakin cutie....such a doll...so mysterious....so dark and beautiful..............

(ok........everybody...i'll stop..........sorry...[ s].....i hope i have not made anyone sick to their stomach....)

But isn't Gene Barry in Prescription: Murder the best of the lot? The conversation he has with Columbo in his office in which he explains how clever the murderer is and why he won't get caught is a speech all of the Lt.'s adversares could have made--the ****ed arrogance! And he strangles his own wife and has plans for a similar demise for his accomplice girlfriend? All the murderers were good, but Barry tops them all.

Thanks to all of you for your interesting comments. It is a difficult, if not impossible, choice to make with so much high-calibre talent to choose from. Perhaps I should have split the title into 2 categories: Serial Killers & One-Offs. Since I posted my comments yesterday, I'm slowly (and reluctantly)edging Robert Culp out of my original 3 and it's becoming a contest between McGoohan & Cassidy. This is a personal choice, and I welcome any and all differences of opinion. I think even the hardest, coldest Columbo killer has to have one or two good "squirm" scenes where our hero has caught him/her off-guard and he/she has to be seen to change something they've already said. For the One-Off killers - my candidates would be Gene Barry, Laurence Harvey, Patrick O'Neal, Leonard Nimoy, and Ross Martin. I know I have ommitted many other wonderful performers such as John Cassavettes, Eddie Albert, Richard Basehart, and Martin Landau. But for me, a great Columbo killer has to be dripping with upper-class superiority and snobbery to contrast our bedraggled hero, and I think the people I've mentioned have that quality in spades. Thanks once again for your fascinating comments - keep 'em coming.

Although many of the killers were played by outstanding actors (Jack Cassidy, Robert Culp
and Clive Reville being among my favorites),
the best combination of actor along with outstanding plot
(with premeditated murders being better than
sponataneous ones) were Robert Vaughn ("Troubled
Waters") and Dick van **** ("Negative Reaction").
I might add Lee Grant ("Ransom for a Dead Man")
although her performance was not quite up to those of the other two. These arrogant killers are all totally cold-blooded assassins.

There were many performances ranging from good to absolutely superb in the villainous characterisation department.

For me Jack Cassidy's characters had that quintessential smugness and self-satisfication that set him apart from the others (however he did get three tries at the villain!).

If you look at the one-offs, I thought Oskar Werner was remarkably cold (without even trying) in "Playback". Leonard Nimoy was also superbly cold in "Stitch in Crime."

Perhaps the most underestimated/underrated performance was from Laurence Harvey, whose initial jitteriness dissipates into ruthless and calculating behaviour, in "The Most Dangerous Match."

To answer the original question my favorite would be Robert Culp. He was great in Double Exposure(my favorite)and Death Lands A Hand. He did what he could in the Most Crucial Game which was a weaker episode.
Jack Cassidy is good but I don't know he seems to just be playing Jack Cassidy sometimes. Two of his roles are almost identical(Murder by the Book & Publish or Perish) but Now You See Him was his best to me. He did a good job in that. He's the 2nd best of the three.
Patrick McGoohan is good but hes a bit eccentric to me. He was very good in By Dawns Early Light (emmy nomination) but I didn't like him in Identity Crisis too much.(a bit weird)3rd.

Some other favorite villians of mine would be: Roddy McDowall, William Shatner, Ricardo Montalban, John Cassavetes,Trish Van Devere(favorite female) ,Donald Pleasance,Clive Revill, Martin Landau, & Robert Vaughn.