There's been so many great villians - Gorgeous George, Ric Flair, Eddie Guerreo, The Undertaker, The Rock, Kurt Angle, etc. But my personal favorite heel is this man, particularly during his first and second WWF World Title Runs in 1999.
I was new to wrestling at the time and he was everything a heel should be. He had Chyna as his bodyguard at the time. She'd interfere in his matches, giving low blows, attacking with sledgehammers, etc. I thought HHH and Chyna made a pretty good team. Having a muscular woman cheating for you? It was unique at the time.
I respect him for not being a coward either. He was pissing off everybody! After Summerslam '99, so many people were after HHH - Stone Cold, The Rock, The Undertaker, The Big Show, Kane, Mankind, The British Bulldog, etc. It seems everyone wanted a piece of him. Everything from "crippling" Stone Cold with a steel chair at Summerslam, to having Chyna hit Kane with a sledgehammer in a title match, to burying Mankind alive in a buried alive match (a match HHH had no business interfering in, btw) The Game knew he was a marked man but often attacked his adversaries first to get an edge.
Almost no matter what his opponents did, Triple H was almost always a few steps ahead. I was sad when he dropped the title to the Big Show at Survivor Series that year. To me, HHH was exactly what a heel should be and remains one of my favorite wrestlers and WWF(E) Champions.
If I had to do a top five it's be like this.
1) HHH (for the reasons I just explained)
2) The Rock - Loved him in The Nation and as The Corporate Champ. I also liked his 2003 heel run. The cool thing about The Rock (especially during the late '90s) was that his character worked the same way as a heel or a babyface. He just didn't insult the fans as a babyface. Otherwise, same guy. Same $500 shirts, catchphrases, etc.
3) Kurt Angle - Overall, I found Kurt Angle too silly to hate, but that love triangle with HHH and Stephanie made me dislike him. A wife stealer? That's something that people will surely hate you for. I also blame Stephanie for letting it happen.
4) The Undertaker - (1999) When he was the Leader of The Ministry of Darkness he was awesome. Sacrifing people? Brainwashing them? Taking their souls? Pure evil and scary. Great character.
5) Jeff Jarrett (1999) When he was on that male chauvinist kick with Chyna in '99, I remember thinking, "Boy, this guy is never gonna get laid saying this stuff!" lol.
Oh yes, and an honorable mention to the late Big Bossman and his poem about the Big Show's daddy being dead.
Who are heels who received legit boos? HHH is one that people love to hate. When his music hits, he always gets a cheer followed by a series of boos. It's almost as if people hear the music and go, "Oh my God! HHH!! Oh wait, he's the bad guy. I'm supposed to boo him. BOOOOOOOO!!"
The Rock is another one who got booed as a heel but it was never real hatred. Jericho is another who still got cheers despite what he did.
Triple H had been a mid-carder for so long that I didn't really take him serious when he finally had a run as WWE Champion. He always had great chemistry with The Rock and Foley but seeing him fight each week with other top stars like Taker, Kane, Big Show, etc, took some getting used to.