Lord: Ephraim. I like Eirika's route more but Ephraim is just such a fun unit to use, being a non-sword Lord with amazing stats.
Cavalier: Franz. Fun unit to train up, and I like his support with Amelia.
Myrmidon: Joshua. For some reason Marisa is the one female myrmidon I really don't like, even though she's kinda similar to Fir, who is one of my favorite characters in the whole series. Joshua has great relationships with other characters - I particularly like his history with Caellach.
Thief: Eh I really don't like either of them. Probably Rennac because him being dragged around by L'Arachel is funny at least some of the time.
Archer: Don't like the archers either, but I'll pick Neimi since she's not a massive prick like Innes.
Mage: Lute. Saleh is just not-as-cool-Pent.
Holy: Natasha
Macho Man: Gerik
Flyer: Close between Tana and Cormag...gonna have to go Cormag because of getting his revenge on Valter and also his supports showing his softer side (he saved a kitten and brought it to Natasha to heal!)
Trainee: Amelia
Other: Tethys. I prefer dancers that have more of an outgoing personality like her, Lalam, and Sylvia to more shy ones like Ninian or Olivia.