The original anime doesn't follow the manga, while Brotherhood follows the manga. I think bạn should watch both. The original anime, despite not following the manga completely, is incredibly emotional, though it's also very dark as well. It's amazing in my opinion. Brotherhood is thêm humorous and less dark, but it's great as well! But yeah, in my opinion, bạn should watch both. The thêm Full Metal Alchemist the better, right? <3