P1 - Loki - it s not close. Well acted, and he stuck around for character development.
P2 - Loki (you forgot him), but Ultron if you insist I stick with your list. I liked Ultron because I like James Spader.
P3 - Hela, well acted and she was the first Marvel villain to just be a BADASS. She was arrogant but could back it up.
Look, Marvel is doing great, but one of the things they and other superhero movies/shows are doing wrong is following the "Villain must die at the end" trope. Loki is the only villain they let live, he s the only villain who has gotten any character development, and therefore is the only villain of any quality. Thanos and Hela got a little more room to be good, but most of these villains are cardboard cutouts that are murdered by the end of the movie.
Marvel should THROW AWAY this trope. Make your villains as interesting as your heroes, and let them survive. I m not saying that every Spider-Man movie should be about the Green Goblin, but he doesn t HAVE to die at the end of the movie every time. He doesn t have to be in the next movie, but maybe reference him, keep him in the public s mind. BUILD their profile.
Batman gets all this credit for his impressive rogues gallery, but if you REALLY look at it, his rogues gallery is kind of crap. A clown, a guy in a tuxedo, a dominatrix, and a guy who tells you what crime he s going to commit before he commits it. But Batman in the 60s made them FAMOUS by using them over and over again. And their fame makes Batman, who really isn t that great or interesting, look more interesting because his villains are famous.
Marvel needs to do THAT. Marvel need Magneto, Dr. Doom, Loki, Green Goblin, Hela, Kang, Thanos and other signature villains to come around and be awesome and STAY. Don t kill them off.
Look at the Netflixverse branch of the MCU. Daredevil is actually a mediocre show, but the villains for Punisher and Kingpin were AWESOME. So well done. And both are still alive. Jessica Jones herself was kind of a mediocre character, but Killgrave was delicious. Allons-y! Strong villains are SO important to a superhero. Marvel has been thriving because of the great humor and action beats, but their movies would have way more staying power if their villains didn t largely SUCK.