If this thread is only supposed to be about cis male options then I don’t think Seiya should count considering their gender ambiguity in the 90’s anime (and they’re outright cis female in the Manga) so they’re immediately out.
As far as the options presented I immediately voted for Ail, while I mostly ship UsaRei in the 90’s anime if I had to pick a guy for Usagi, Ail is clearly far-and away the best choice, let’s recap shall we?
Ail is:
1. The closest in age to Usagi after Umino being only 1 year older than her so they’d be pretty much on the same maturity level which would make for a far more equal dynamic than the one 90’s anime UsaMamo have.
2. While technically “a bad guy,” is definitely one of the most redeemable and reasonable “bad guys” the franchise has ever had. Ail & En are doing what they do out of sheer survival, nothing less and nothing more. Their is no malice involved in their energy-sucking, no ill-will towards their victims, they are simply energy-sucking out of ignorance because they literally don’t know any better or of any other way. Once they do learn of another way though (Ail especially) they are able to fully redeem themselves and take that non-violent path. In fact I would go as far to say that this aspect of their characters makes them come off as less villainous than even anime Haruka & Michiru. (Who despite being shown alternative non-sacrificial methods countless times still persist in taking the “morally grey” path.) If Usagi’s going to be with anyone, it should at least be someone whose moral compass most strongly aligns with hers. She may be an all-forgiving redemptive Jesus in the 90’s anime but even I wouldn’t pair her with a literal outright former villian, and no I do not count either Ail or En as true villains in the literary sense - they’re antagonists certainly but antagonist is
not the same as villian. She needs someone with at least the same values as her who don’t find joy in doing harm.
3. Actually interested in Usagi, and unlike either Umino, Seiya or Demande is
not a creep about it! (And the other guys on this list aren’t interested in Usagi at all) Sure he’s still pretty forceful and direct, but his forcefulness leans more into endearing and just outright socially acceptable courting compared to all the other people who vye for Usagi’s affections. Umino before he gets with Naru is a perverted stalker who voyeristically peeps on women and takes pictures of them without their consent, (and even when he does get with Naru, his behavior towards her frequently crosses boundary-breaking lines into outright creepy territory.) Seiya in the 90’s anime is the very template for the guilt-tripping “nice guy” trope, who thinks they’re owed a girlfriend, and do I even have to
explain Demande? Meanwhile all Ail does is genuinely sweet gestures such as offering to play/compose a song for Usagi on his flute and brings her a bouquet of roses declaring his love for her - he never attempts to ever go any further than this in his courtship of her and is generally normal and respectful all around.
4. And my final point in favor of Ail, perhaps the most important one is that Usagi was also interested in him, they were both
mutually crushing on each other. Unlike all the others on this list it was never one-sided, they were immediately attracted to each other, no doubt she would’ve eventually started dating him if she hadn’t gotten her memories back, and I was disappointed when the narrative never made this into a genuine conflict and dropped her growing crush on him to never speak of or acknowledge it again come the very next episode. Why did she just have to give up her very genuine and normal schoolgirl crush on Ail to chase a guy that she never even really liked? Just cause of their now non-existent past lives or because the plot said so cause we need to keep the status quo? I actually felt quite sorry for Usagi as it’s obvious Ail would’ve been a great boyfriend to her, much better at least than 90’s Mamoru could ever be:
Now you may be thinking but Tsun, what about En? And to that I say that just like I don’t think UsaMamo make a good couple, neither do I think are Ail/En a good match for each other. Their relationship has obviously become toxic and on the rocks if they can both get such wandering eyes for other people and are apparently a-ok with blatantly cheating on the other out in the open like that. It was immediately obvious to me when first watching that arc that they had both simply outgrown their relationship and it was time to move on to newer pastures, they’ve been together so long and were all each other knew and they were getting quite a bit antsy. How many people do you know end up with their first significant other for a lifetime? Not many right? Especially at such a young age Ail & En have been together since. Similarly to UsaMamo it feels like Ail & En are only together because they feel like they had no other options, but as soon as they find a planet with an abundance of options, the cracks in their relationship immediately begins to show and it’s fragility is exposed.
Storywise I think Saphir would be a very good choice. He is nice and calm, would suit Usagi well. Also as Black Moon Clan leader's brother, it could create a lot of drama.
This is like one of the crankiest crack ships I’ve seen yet lol, 90’s anime Saphir literally
hates Usagi out of jealousy and views her as a rival for Demande’s affections he says so himself in episode 83.
And as for Manga/Crystal Saphir, he’s so bats*it insane & evil to begin with he would sooner
kill a woman than
date her, as demonstrated perfectly when he goes all psycho on Usagi and even tries to kill his own brother!
Maybe Artemis could match as well? He is nice and funny, also sometimes goofy.
Human Artemis is for Mina though…