No mention of Donovan’s Reef? It wasn’t a great movie, but it had Marvin and the Duke together, their characters meeting up for an annual birthday brawl.
It is simple, Marvin was a better actor. Wayne had developed a single character which he did well, but he didn’t have range. Marvin had his limits too, his characters didn’t range far from his own personality, but Cat Ballou showed he could harness that effectively.
You or golden?
I’m only guilty of the last one on the list. 
To me, this is a key point. Wayne needed to have a movie built around him. Marvin could be put into a movie. This, to me, says that Marvin was the better actor.
Well, in Wayne’s own words: “I’m not an actor. I’m a re-actor.”
I always forget: is that the one where, toward the end, Wayne and some other guy explore a sunken ship and wrestle with a big puffy octopus?
Whichever movie that is, it’s fun. It jumps from a somewhat staid courtroom scene to a diving-suits-and-helmets scene. Also, John Wayne is pretty much the bad guy, which wasn’t usual for him!
Ah! Reap the Wild Wind! I always mix up those titles! “Never mind.”
A simplistic, but not inaccurate, summation: Lee Marvin was the better actor, but John Wayne was the better movie star.
On a so-so or better day, Marvin was much, much better than Wayne on a great day.
The problem with Lee Marvin was he drank way too much and sometimes cared too little and this would lead to too many less than good performances.
Wayne was fairly consistent. Too consistent. He just didn’t put it out all on the line, take real risks, etc. He played it safe.
A Dirty Dozen with Wayne would have made the critics’ top 10 worst films of the year lists.
I haven’t seen even a majority of the movies these two guys did, but I have seen the ones listed by the OP and many of their better known films.
To me, it’s almost an apples-and-oranges type of comparison.
Both were very good at what they did, and usually stuck to roles that fit their style and talents.
I think, as far as range was concerned, that Lee Marvin was a bit better actor than John Wayne. He had that menacing look and aura to a lot of his portrayals. Sure, you knew that Wayne would eventually get fed up and punch you in the face, but with Marvin, you were never sure if you would know when or what direction the punch would come from.
Wayne, however, was the master at playing ‘John Wayne’. Face it, that was what the public wanted to see. No one played ‘John Wayne’ better than john Wayne, and that was what he brought to the role in spades.
I was never a fan until I saw Stagecoach and then I understood why John Wayne became a big star.
For what it’s worth, Lee Marvin was quite good as Hickey in the movie version of Eugene O’Neill’s “The Iceman Cometh.”
That was a role John Wayne wouldn’t have understood, let alone tried to play.
But fortunately for him, and everyone else, Wayne was the spitting image of Genghis Khan! 
I wonder how much of his difficulties could be traced back to his military service. He joked that he was shot in the ass but in reality a machine gun bullet severed his sciatic nerve. Heavy combat, badly wounded and almost no mental health care for WWII vets was a bad combination for many.
lol (+1)
Possibly. He was known as a drinker when he first began acting after his service. But I recall somewhere that he came from a family of loud, carousing, drinkers. His wiki says he was expelled from several schools before his service, so injuries may only have exacerbated an existing proclivity.
He got his first role standing in for an actor when he worked as a handyman at a theater. When the actor didn’t show they needed someone who could play his role as a loud obnoxious character. That fit Lee’s personality already so they asked him to give it a try.
I bet Wayne was a better singer.
“They call the wind Mariah, Pilgrim.”
You obviously weren’t born under a wand’ring star.