Vienna Genesis
Personally, I vote Brotherhood. And, furthermore, I do not even think the two SHOULD be commonly referred to as "FMA" and "FMAB" because that implies that Brotherhood is not truly FMA. And I happen to think it is the ONLY true FMA. Thoughts?
IDK about that I'm not that big of a FMA fan but Brotherhood just seems to be like FMA form 2003 with a few more additions. One I've notice is Major Armstrong's other sister, the mini panda, and the 2nd Greed are all I can think of right now.
There not that much different but I see FMAB as more of an AU from FMA since if came out first on air.