Looking at each wrestler in their prime...let's say 1995. I'd no doubt book Sting as the clean winner versus either man. He was the perfect combination of strength, power, technique, speed, and high-flying maneuvers. He was the perfect mixture of Bret Hart and Shawn Michaels. Not saying I don't appreciate the prowess of HBK, but most of his key victories for the World Title during the nineties involved cheating or a fluke call...typically against Bret Hart no less. Referees hadn't established the concept of the overtime periods in the Ironman match at WMXII and Michaels would've either tapped or been knocked out whilst being deadlocked in the Sharpshooter. We know how it went down in 1997, so I'm not going to waste effort typing about it. Undertaker has never been anything electrifying in a ring and even though he holds victories over Nash, Sid, and the Big Red Mistake, he's hidden behind a gimmick to cover up for a lack of wrestling ability. Being big and rolling your eyes back in your head hardly makes you a wrestler, let alone a decent one. This is why I'd have chosen the Stinger. As for a current match? I'd book HBK as the winner. He's kept himself in better shape these last few years as Sting (as much as it hurts me to say) has kind of let it go. Currently for a match with Sting versus the Undertaker? Either guy would be fine to win for me. Sting still is strong as a bull and even in the late nineties he could slam the Big Show (which was strange to see...and amazing).