I love Eddie and Al so much I can't really describe it. Seriously, they are one of the coolest duo's ever. I never ever get tired of them.
Mustang and Riza are another two favorites. They just get to be more and more awesome with each volume. They didn't even blow anything up in this one, and I'm still grinning like an idiot every time one or both of them walks onstage.
The other characters I haven't mentioned yet are also great. Envy is a super-mega-ultra-
The characters I don't really like are: Ling and Mei. I don't dislike Mei, she just doesn't have much personality yet beyond random bubbling. The way she's drawn is cute though, and I love her little panda-monster. But Ling - I actually do not like him. Characters whose eyes are always closed irritate me for some reason - both in here and in Black Butler, there are characters whose eyes never/almost never open. It drives me crazy, they always look the same no matter what their facial expression is supposed to be.
Also, he's just plain annoying...
The only character I hate is Hohemheim, Al and Eddie's dad. I detest that man. He's whiny and sappy and ungrateful and self-obsessed.
Probably not. Al's too nice for his own good. And too forgiving.