Ling - because he can pull off funny
and bad-ass in 2 minutes; seriously, first he's all relaxed and comical and then he starts fighting
Hohenheim - I call it the 'aura of awesome-ness'. In other words I'm not sure why I like him, he just seems like an interesting and important person (he's the main characters' father who mysteriously disappears all the time...)
Havoc - He's just so likeable and I can't help feeling sorry for him. Comical relief sometimes but not hollow like most support characters in other anime who serve to this purpose.
Father - I've got the feeling I am going to like him.