I LOVE Clint Eastwood and his efforts in the "Dollars" trilogy singlehandedly define the sub-genre for the more casual observer. BUT, he was only in three Spags. Three of the finest films of their time of course, never mind "westerns", Eurowesterns" or any other label, yes. But still only three. If the question posed extended to all western movies then Clint, for me, would be a lock. But regarding Spags alone, I have to go with LVC. He's arguably the more intriguing character in both TG,tB&tU and FaFDM, so even if that was all he'd done there would be a case to me made for him over Mr. Eastwood. But on top of those two leviathans you can add The Big Gundown, Death Rides a Horse, Day of Anger, The Grand Duel, Sabata... that's Spag Nirvana right there, and LVC is the most compelling factor in all of them. His face is the very personification of the deadly, mythical West the Italians created.
And his hairstyle alone in God's Gun was more badass and deadly than John Wayne EVER was.