Brotherhood. The first series was poorly written with little care given to continuality and characters
i believe it all depends on your personality. for me, its FMA 1 all the way. i find it much more creative than FMA 2 since it just copies the manga (and the original FMA is so holy to me i'll only read it book-wise). it has the characters develop entirely differently than the manga (although i haven't read all the book yet, i have seen enough) and it just blows me away that the writers could keep doing their awesome job for 5 whole seasons and not lose their gift. writing an entirely different storyline and still getting a huge success from it for 5 whole seasons compared to just a copy of the manga a few years later is much more impressive to me.