1. Xane: He is really unlike any other Fire Emblem unit. Want a clone of your best unit? Go ahead. Want to get a third ballista? Go nuts. He's just really fun to play around with, if a bit more harder to use than a traditional dancer.
2. Sedgar: Yeah, training him up is only worth it if you don't mind shitting your turncounts, but if you don't then you get a unit with the best growths in the game! Besides Wolf, but his hair is dumb :P. You'd be surprised how long a capped defence general can get consistently tinked.
3. Jagen: Base B lances, with you for the entire game, cool shoulder spikes, what's not to love? It's not like he falls off that hard, reclassing and forges allow him to stay relevant for a long time.