Undertaker, do doubt in my mind, ive seen his last 5 WM's and I gotta say, im pretty impressed.
I'm not going to call you out or anything because your entitled to your opinion, but I'm going to respectfully disagree. I think within Kayfabe there is no doubt that Undertaker is Mr. Wrestlemania because he's undefeated. Also there's no denying that he puts on great matches and with his gimmick he really makes people pay attention with the entrance and everything.
Here's why I think that HBK is Mr. Wresltemania. Take last year for example. Taker-Batista was a hell of a match, very good Taker won. HBK took on Cena and lost, but when the show was over you would have thought HBK won because he stole the show and tore the house down. That's what makes HBK so special. At any PPV, not just 'Mania, if he's on the show and he's into it(which he usually is) he has the ability to completely take over. Even if it's a non-title undercard match if HBK is on his game he'll leave everyone talking about his match.
Another reason why I think HBK is so special is that excells in all matches. If you look at HHH, Taker, and even Jeff Hardy(I'm not putting him in the same class as those two I'm just using it as an expamle) they put on great shows, but when they put there best matches on in HIAC, Cage Matches, TLC's, etc. HBK has the ability to take the show over in a normal, classic one on one match. Obviously he does well in other matches, but he takes the show over in regular matches. When you look at the other one's great matches we all remember their matches in stipulation matches. Some of HBK's best matches are just regular ones. And I think that is why HBK rules over the other ones. Undertaker isn't a bad choice, but I think you have to say HBK is Mr. Wrestlemania.