My favorite definitely had to be Claire. Jerry Jewell was the perfect Claire, with the right amount of swagger and sexy accent. He even changed his voice a little when going into the Rail Tracer persona. (And watching episodes 14-16 again reaffirmed my love for Claire himself. He is just the right combination of dorky, crazy, and badass. ♥)
I also grew to like Ladd's dub voice. Once I got over how different he sounded from the Japanese, I thought he did great in the role. Czeslaw, Elmer, Huey, and Dallas impressed me too. And many others. God, this show has a ton of characters.
Chris Patton's Graham wasn't as good as Tomokazu Sugita's though. He did fine, but Sugita sounded more batshit insane and hilarious. Kinda the same problem I had with Isaac and Miria in the dub; the Japanese performances were hard to top.
...Oh man, new FMA soon. *__* SO EXCITED.