My vote would go to 08/09 Jericho.
I've yet to see someone reinvent themself in modern days as a heel by actively doing things against the fans.
Started wearing suits.
Changed from long tights to unfamiliar trunks.
Ceased running the countdown clock for his entrance.
Stopped his signature taunts and sayings.
I believe he once also described that when he called someone a "gelatinous tapeworm" the next week he saw a fan sign with that written on it. Then and there he made a mental note to never say it again.
Not to mention his incredible heel entrance at 'Mania 26 where he literally just walks to the ring. No showboating, no fan interaction, just a normal walk. Mania entranceways are long too, and he stayed the course. Just wish he didn't have pyro.
I give Miz credit. I was a massive anti-Miz man prior to his A-Lister run. Everything before his current run made him look like a mark's create-a-wrestler from a video game. Flashy and cool with his 4 motion-captured taunts. Nowadays he seems like he finally has it down.