I voted for Django the Last Killer but Hole in the Forehead is maybe equally good. I also liked Pistoleros, I need to rewatch it some day.
Last Killer rose above Forehead in my recent Top 20 - and I loved his mentor part, he really gets his teeth into this role. I like him a lot in all of these really, with Tequila Joe being my least favourite... for reasons I've already discussed on its thread. But Ghidra is a superb fellah for the genre - great face! 8)