I'm a big Fordola sucker, so I'd go with Fordola.

I know she doesn't seems appreciated, most of my friends don't.

Since EW will march to Garlemald, I would expect Gaius to be the "guide character" like how Lyse narrated Stormblood or Ardbert did Shadowbringers.
But in an interview, Yoshida mentionned that Gaius would have a role but not a big one. So I doubt he'll be a Trust.

Also for trusts, I'd like for them to buff their damage. I found out that it was better to let them do the job each pull and AFK or something, because they'd simply use their overpowered actions.
A dungeon would take 25 minutes with trusts while helping them as a tank, 30 doing nothing except for mini bosses.