I limited it to TV because otherwise we’d be here all day. I was inspired by watching “Have Gun Will Travel” on DVD. Could Paladin beat the Lone Ranger? Feel free to throw in your own candidates.
I remeber a scene on Gunsmoke, where some bandits saw Mat Dillion coming. The leader told the others to hide while he went and talked to Matt, with instrucutions to open fire when he removed his hat as the signal. As he and Matt were talking he moved his hand off his pommel, and Matt casually said “you touch that hat and you’re a dead man.”
I thought that was pretty cool.
C’mon, it was the Rifleman.
Second The Rifleman. He pretty much wacked at least one guy per episode.
None of those series guys, including Cheyenne Bodie, held a candle to the Lonesome Dove main charcters played by Tommy Lee Jones and Robert Duvall. They were modeled on some real-life men who were even tougher.
Steve McQueen in Wanted: Dead or Alive was pretty quick but in the end I think too young and therefore inexperienced to get the nod. Palladin made too tempting of a backshot target, what with all the black and silver. Gil Favor in Rawhide rarely pulled his gun, instead defusing danger with character and reason. The Lone Ranger was always so keen to be good that I could see someone getting the sneak on him, that despite Tonto’s best efforts. The Big Valley boys were all a bust.
So yeah, Lucas McCain or Matt Dillon. Probably Dillon because that dumbass Mark McCain was always wearing Lucas out doing stupid shit.
He doesn’t play a real cowboy on the show, but his wearing a cowboy hat is enough for me! I love to watch Chuck Norris on Walker: Texas Ranger! 
God bless you and him always!!!
Holly
I don’t think any cowboy got shot more times than Matt Dillon. He had more holes in him than the Operation Game dude. I gotta vote for Matt for this.
Matt.
Which is why I disallow him. Lucas didn’t allow himself to get shot so capriciously. Nick Barkley was a bit of a badass. I loved Gil Favor but not aggressive enough. Early Lucas is a winner hands down.
McCain.
Captain Mal Reynolds, obviously. (Hey, it’s a space western–that makes Captain Tightpants a… space cowboy?)
The classic TV westerns were all way before my time, and too “white hat/John Wayne”-style for me, a spaghetti western fan. The only TV western I’ve ever liked is Bonanza, and I don’t think anyone’s going to make a serious argument for Hoss as the toughest TV cowboy.
Funny you should say that, because I was just about to offer his name. He was easy-going most of the time, but you did not want to get in a fight with him.
The other guy I was going to mention was Rowdy Yates. I don’t remember much about Rawhide, but the OP disallowed movies, and the guy who played Rowdy is the guy I think of when you talk about toughness, considering how many times he got beaten to a pulp in the Leone movies, and then bounced back to kill everybody involved.
Yup.
Cowboy Curtis in a walk.
OK then, Porter Wagoner.
Lucas McCain killed more people than small pox.
He who turns and runs away, lives to run another day. Brett Maverick
I’m going to go for Kwai Chang Caine, who frequently took on gunfighters with only his bare hands, walked the old west barefoot, could move burning braziers with his forearms, took an arrow through and through and could catch a thrown hatchet.
Just because the show was set during a certain time period does not make him a cowboy.
If Porter has even worn a hat, I have yet to see a shot of him with one on his head, may he rest in peace. Of course them flamboyant suits that he wore is what he is known for more. 
God bless you and his family always!!!
Holly