Shonen is the most popular genre of manga/anime, which is typically geared toward action/fighting but often contains a sense of humor and strong growing friendship-bonds between the characters.
Tough choice, but FMA is definitely my favorite on that list. Followed by One Piece and Naruto.
FMA for me. I will never even touch an anime that's more than 200 episodes. FMA is one of the best mainstream shounen titles precisely because it's not milked to death with unnecessary filler-episodes and whatnot.