Really though, if it came to only getting ONE FFXIV Chaos Rep I'm honestly not sure.
I listed Lahabrea because despite him being a jobber, he's the one Ascian you fight near consistently, and Ascians are (Unfortunately) still a major plot point, and his playstyle could be unique
But then you got Gaius Van Baelsar who's cool as heck design wise, and has some good motivations, but he also had some major jobber moments before jumping into Ultima Weapon, though, his EX Burst mode could be him getting the golden pimp armor he got before getting in Ultima Weapon (Plus, he was on the friggin' cover of FFXIV Original)
Nael Van Darnus would also have a unique playstyle as well as a good EX Burst, but most people wouldn't really know who she is, and her story is basically lost to 1.0 and a Raid too hard for most players to indulge in nowadays
Zenos Yae Galvus would, again, have a cool moveset, what with the three swords and implied Bushido/Samurai Swordplay, but the major issues with him is that he's the major villain of Stormblood, which isn't even 3 months old yet, his moveset as well as some other tidbits would more than likely be spoilers, and I think the window for spoilers with a Dissidia character is rather large (2 years, I'm guessing?)
So Realistically I still think Gaius is the most likely choice.