Heel HHH. When he won at Wrestlemania 2000 it was the first time a heel had won in the main event at wrestlemania. When Austin turned heel at wrestlemania X7 it marked the second consecutive Mania where the Rock had been screwed out of the WWF championship by Vince.
Since then a babyface has gone over in every match in the top spot at the grandaddy of them all!
Heels have won title matches since then but never in the last match on the card. Unless you include when Cena has won as he almost always gets Booed out of the building at The Big One ; )
In My Humble Opinion, the most despicable finish to a match at Mania occurred when HHH crushed Booker T's hopes of becoming the World Hearyweight Title. Despicable for two reasons. Firstly, it took Vinnie Mac's Favouite Son around 30 seconds to make the cover on poor old Books after The Match Winning Pedigree! It made Mr Huffman look like such a chump, the skinny old lady in the third row would have kicked out of it!
Secondly, Booker got the title shot by winning a 20 man Battle Royale on Raw. Last eliminating SuperNovaHeel Rock who had been distracted by The Hamburgle.... Oops, sorry, By the Hurricane.
After the BR he was on fire! The fans were finally "Digging It". Then they brought up his past (robbery, prison sentence) and The Tripster played the dreaded race card, There was no way in hell Booker was going to lose that match. He had to win that match more than any other wrestler had to win a match in history!.... But he never.... After that Booker T was never seen as a real title challenger until he became King Booker years later.
It was a travesty, but nothing more than a day at the office for the political nightmare that is The Game.