I voted for Last Temptation because it's clearly great.
And while Passion is an absolute disaster and a bad film, it's still super duper fascinating to me in perhaps all the wrong ways. It's a superb document of an artist melting down at 24fps. If this was a solo and not a vs. ep, I could maybe see myself voting the Passion into the canon for similar reasons as Clerks.
Gibson's idea to shoot it in a dead language feels 1000% like any single dumb film that comes along where its director is all "I wanted to examine what XYZ would be like if it happened for real, right in front us and what that would be like to capture it on film" as if they're the first person to invent verisimilitude in cinema (and bootstrap it to the fantastic or popular myth and stories). This actually feels sort of Iñárritu-y to me*, where someone makes a decision and it's purely technical or a blanket method of execution and not something that's creatively driven/sound or conductive to theme and emotion. It's a sense of 'realism' that's very surface and not something the film applies to itself for thematic purposes. It's a layer of artifice, regardless of intent. It actually betrays the intent of aiming for verisimilitude.
*Speaking of artifice and audience barriers: I had huge flashbacks to Passion when watching The Revenant. Glass crawling to a creek, drinking water while having it spray out of neck, and the him stuffing gunpowder into his throat felt kinda like the moment where Christ gets his shoulder dislocated. At some point this goes from 'gruelling' to 'maybe this is sorta silly' and I can see some common DNA linking the two.
Also, in terms of who this is for, how it plays and the BTS narrative of its production, The Passion Of The Christ might be the ultimate fan film. From the narrative of "No one would let me make it my way, so I decided to make it on my own terms and with my own cash, baby!" to the feeling there's no sense of self-imposed boundaries/goals in play or the question of "what is this really about and who is it for?" that creatives should ask themselves occasionally. Gibson made a passion play, and a passion play it is for people *really* into passion plays, but it serves no function or idea beyond that. It's a framework that holds up very little beyond its own rather wobbly framework. Fans got what fans wanted from a very big fan because no one was there to activate the "audience want vs. need test." Very proto-kickstarter!
