Musashi, without a doubt. Conan has strength, but little skill. Musashi did not kill Inigo's father, and so would easily defeat the revenge-driven Spaniard. Yojimbo? I honestly don't know who that is. Robin Hood was tops with a bow, not a sword. Zorro is too wussy. Connor McLeod has near-invincibility going for him, but if Musashi knows how to kill him, he can do it. Leonardo would tell you, I'm sure, that he's a student of Musashi... not the master of him.
Regarding Yojimbo, Wikipedia is your friend.
Most know the name from the classic Akira Kurasawa film, Yojimbo, which inspired later films such as "For a Fistful of Dollars" with Clint Eastwood and "Last Man Standing" with Bruce Willis (both of them were practically 1:1 recreations, just in different settings, and both credited the Kurosawa screenplay). The sword work in Yojimbo is some of the best ever filmed.
Connor McLeod has near-invincibility going for him, but if Musashi knows how to kill him, he can do it.
First of all, I doubt Connor would tell his opponent how to kill him. Part of his power lies in his secret: Connor is an ordinary looking guy who just happens not to die unless he's decapitated. That's just not the sort of thing Musashi has trained to expect when he designed his fighting style.
Musashi will probably die before he figures it out. Remember, the Japanese swordmaster's philosophy: when you commit, put everything you have behind it until you win. Connor has literally centuries of training: he can fight in Musashi's league, and would cut Musashi in half once Japanese blademaster committed to an overwhelming attack that would have killed anyone but Connor.
Even if he knows Connor's weakness, it won't be easy.
From the Japanse sword techniques I've seen, no swordmaster, let alone Musashi, focused their training on a horizontal cut at head level: it's just too easy to block.
Japanse swordwork emphasises cutting the skull in half, slicing the body diagonally to shatter the collarbone, cutting up the hands and tendons, etc. None of those work on Connor.
Connor McLeod just has to hit Musashi anywhere, and Musashi will bleed until he dies. It won't take long.
Musashi has to land powerful killing stroke at a target he isn't used to aiming at, against an opponent who's trained for centuries to block that very strike.
Musashi's victory is anything but guaranteed. I say he'ld be sliced to ribbons.
Any (to a normal mortal) fatal blow to Connor will disable him long enough to deliver the (permanently) fatal blow.
I don't think that's true.
In the film, we witness a rapier duel, where Connor is run through the heart several times, (certainly a fatal blow to any other mortal), while Connor just stands there, drunk out of his skull, and laughing manically at his bewildered opponent. Eventually Connor gets bored, staggers off, and mutters his apologies to the frustrated duelist...
We watch him cut his hand open, without showing signs of significant pain, or going into any form of shock, and we watch it heal completely in seconds, which is admittedly a long time in a duel. If Musashi cut him in half, Connor would probably just blink, and cut Musashi in half in return before Musashi could pull his sword out.
And it's not even guaranteed that Musashi is a better swordsman: Musashi only knows how to defeat the fighters of his day. His "new philosophy" of fighting might be new to the people of his era: but surely not to an immortal who studied swordplay for centuries, exploring every nuance for advantage.
Pain resistance and kill difficulty aside, Connor has explored every sword technique known to history. Musashi only knows the ones from feudal Japan that he personally invented; and his advantages derived largely from his unorthodox style of fighting; his success was as much a result of superior psychology as physical prowess, though of course he was a master of both.
Connor has trained with a view to decapitate; but that doesn't have to be all he did with his centuries of training. He's trained for centuries to find advantage, just like Musashi: expecting to be attacked at any moment for centuries gives one a professional interest in swordplay. Musashi only fought for about fourty years, and his psychological tricks and "unorthodox style" aren't new to Connor...
Well, my take on it is this:
Winning the fight does not necessarily mean killing your opponent, and Connor McLeod is not immune to pain. Musashi could easily lay him open (not fatally, as it would be to a normal man, but fight-winning anyhow.
Also, McLeod may have centuries of training, but he mostly trains to deliver and block decapitation shots.
Don't forget, Connor McLeod has competed in an elimination-style competition system which basically serves to prove who the best swordfighter among the immortals on Earth is. Most of these immortals has had the chance to train with multiple human master swordsmen, so each of their aptitude is bound to be pretty high. Cheating aside, McLeod has more or less proven, by winning the contest, that he is the best swordsman on Earth.
My take on the Robin hood thing:
Robin jumps out at one of them, demands half of their possessions, and then spends the next 30 seconds realising that he is way out of his league. He then cries "Wait!" and determines he opponents identity, whereupon he claims some sort of spritual kinship, offers them a drink and meal down at the pub, and suckers them into his band.
Rinse, and repeat.
(cf Gambol Gold and Robin Hood, RH& Tuck, RH& Little John, etc...)
-Reality might not get out of Beta today. (O.Timas, "Bot")