If we're going by the current 3 games then here's what I'd like to see for each:
Fates: Kaze/Jakob, Keaton (Because this game is really lacking in beasts, plus I want to stomp around as a giant wolf) and then Silas as a lance cavalier because we're missing one of those
SD: Camus, Merric and Cain/Abel
Awakening: Gaius, Severa and Inigo
What I really want though are characters from SoV and Blazing Blade
For SoV it'd be: Alm, Berkut and Delthea
And then for Blazing Blade it'd be: Hector, Eliwood and Ninian