[Coldsaturn]

OK no one asked for this but I'll happily scream into the void just to hear my own echo: here's my finally stable ranking of the boys after a fierce battle between n.2 and 3

1. Raf
2. Caleb
3. Sylus
4. Xavier
5. Zayne

This considers both who my main MC romantically vibes with better, who I enjoy seeing with my different MCs, the narrative themes and tropes they use etc. But with just these variables I always ended up with Caleb and Sylus switching place based on the banner, and Xavier battling with Zayne over who gets the best dynamic and plot every other card. Too messy, but not that big of a deal as long as we're in the bottom half of the ladder. The upper part needed to be sorted, though, and after some time spent examining my gut feelings (and watching many tiktok edits) I ended up putting Caleb in the throne at n.2. Why? 
N.1 and N.2 are the guys I truly genuinely do not trust to be normal if they ever lost MC. The others? Given enough time to process and grieve: proper rational adults. Those two at the top? Different shades of completely unhinged codependency, and that's too compelling for me to ignore so Caleb gets the spotlight too.

[ChicletPrime]

(gravely) Always important to consult the TikTok gestalt when you just can't make up your mind.

i have two concurrent lists myself. for how much each guy appeals to me on a combination of levels, but basically boiling down about how happy i am to interact with them in any given scenario. I have the same problem with constantly switching 1. and 2. based on the individual card we're talking about, but brother-con/sis-con just grabs me by the gonads a little harder than demon-lover.

i find it a little amusing that while i started out the game liking Zayne the most out of the first three, he's fallen to last place over time.

1. Caleb
2. Sylus
3. Xavier
4. Rafayel
5. Zayne

but the OTHER list which i actually feel is more reflective is how well i think their characters are WRITTEN - not so much how it plays out in the kindles and cards, but how the characters are set up and how much i think the writers cared to make them interesting and thought-provoking:

1. Rafayel - this boy is an absolutely scary mess
2. Caleb - this boy is a very scary mess
3. Zayne - this boy is such a quietly soft *painful* tragedy that just doesn't get enough airtime.
4. Sylus - a tad too straightforward for my literary tastes
5. Xavier - the most simplistic theme of the bunch - while there are hints here and there of depth (thinking Fallen Crown and some of the Anecdotes) overall he's on-brand Charming 97% of the time

[Coldsaturn]

"brother-con/sis-con just grabs me by the gonads a little harder than demon-lover"
You're so valid for this. What can I say if not "yes"?

I have a love/hate relationship with Zayne because he's not just someone I know I would end up going for in real life, he literally reminds me of a couple of my ex-partners. I fear that's the reason he's so adamantly at the bottom of my ranking, too close to home and I've ended those relationships for good reasons lmao

I completely agree with your second list, I could have written it myself.
I definitely have to give a shout out to Zayne's plot in the story. To me, he's the closest thing we could have to a "protagonist" in this story beyond MC. Every LI has personal stakes and individual conflicts with EVER, but something about Zayne's plot line just reads as the most natural to me if I ever had to imagine a book set into that world (at least as long as we don't touch the master of fate thread, but that's personal taste). Caleb would be a close second, but his chronic lack of content compared to the OG3 (Zayne, Xav, Raf) makes it impossible to reach Zayne's range, unfortunately.
Xavier saddens me as a reader and as a writer because I'm so in love with time-travel stories and yet I'm always left feeling like I'm missing so much angst from him. The latest main story chapter tried to deliver a bit on that, but it's still very far from what I'm craving. He's still stable in my ranking, but I wish infold pushed so much harder with him. Or maybe I'm just not the target audience for his characterization, so I end up not feeling like it's matching the trope to my liking.

[ChicletPrime]

I really think they should have done/should do more with Xavier, but his personality is pretty much locked in stone at this point so our only real hope is a completely unhinged myth.

Xavier threw over / deliberately doomed an entire civilization, mostly because of the main character but its not exactly a stretch to say that he may have done it anyways even if the main character didn't exist. If that whole sequence of him finding out how Philos was keeping itself alive/above the proverbial waters happened in some other manner that did not require a personal connection, I do believe pretty strongly he'd have done it regardless.

But the fact that he DID ostensibly do it for love crams in just a whole lot more angst that just never really appears in his personality. Could he regret it? Does he resent the girlfriend at any point for being completely unaware/unappreciative of what he's done? Does he live in fear that she'll Find Out And Condemn Him? Does he ever wonder if it's worth it, or if he's just fucked things over for no reason? That time is an immutable path that he can never, ever change or circumvent and that when he tried to fix things he himself is the reason for the path to exist at all?

I mean, ten minutes of spitballing things at the wall and you could come up with a list as long as your arm that would spice up Xavier's worldview. Instead he's mostly Sunshine Boy that loves you and only occasionally hints that the clear blue waters of his eyes might possibly contain a black drop off into the Marianas Trench.