I actually never watched FMA....should I watch the old or new version? I've been told the new one is better and that;s the whole point of the re-make but others say the opposite.
I'm siding with the new version.
The 2003 version is MUCH darker, has a smaller cast and more focus on the characters and their struggles, they feel more human, flawed and relatable. It has a better start but is an anime original work after like 40% of the way through due to the Manga not being complete at the time.
FMA Brotherhood is a true shounen, follows the manga, more cheerful and has more characters.
I recommend watching the 2003 version first then the Movie which concludes the story, and then Brotherhood. As Brotherhood was made with the assumption that you saw the 2003 version, it essentially skips ALOT of the story, which makes it difficult to understand at the beginning.