In My Uneducated Opinion
Everything is relative, right?
Relativity makes a huge difference when you see Justice League one night and then Thor: Ragnarok the next morning. After watching Ragnarok I came out saying, "That was SO much better than . . . Justice League."
But in the end, has Thor ever really surpassed his first triumph?
The first Thor movie is the greatest in Marvel's movies. The reason behind it is the complexity of characters. Thor goes through a full character arc - Entitled brat that thinks his power gives him authority to dominate to humbled prince that realizes his power is a responsibility to serve. Relativity being what it is, compare Thor with Thor: The Dark World.
Thor = Character development and arc.
Thor: The Dark World = Flat character. Let's just pretend this movie didn't happen.
Thor: Ragnarok = Different character than we've ever had. But development and a real arc.
Ragnarok starts with Thor serving his father and trying to fix everything. By the end the god that was willing to be a servant and not seek power finally realizes his potential as king of Asgard.
So my opinion is that Thor is the greatest Marvel movie and that Thor Ragnarok is right behind it. There are some major problems (Suddenly Thor is a bumbling oaf, Bruce Banner says if he Hulks one more time he's gone, and then he Hulks . . . I'll just let Cinema Sins take over when they get their hands on it). But other than that, pure story, Ragnarok is the second best Marvel film.