I think the natural instinct for most people would be to say Obi-wan, but I think Jango Fett gave Kenobi a pretty good fight. How much better would Macleod be than Jango Fett?
Remember that the only reason Jango gave Obi-Wan a contest was because he took the lightsaber out of the equation right at the start. As Obi-Wan said, "this weapon is your life." Later when Jango faces a Jedi with his lightsaber, he lasts all of five seconds.
Duncan's sword isn't magical, it's just a really cool sword. A lightsaber would cut it up like cardboard.