I think Fatal Fury has the more memorable and recognizable characters. It's my favorite SNK fighting game series next to Samurai Shodown and King of Fighters.
AOF has it's own unique style that I love (the spirit gauge, jumping off walls, the zooming screen, and useful minigames), but there's just something about Fatal Fury that I love more. It's probably because Terry is just so cool
. AOF does have Ryo, Robert, Lee and King who I think are quite memorable, but Fatal Fury has Duck King, Raiden, Billy Kane, Mai, Kim, Joe, Andy, Laurence Blood, Krauser, and Geese. Both are outstanding games, but for me, Fatal Fury is the true King Of Fighters (I just had to say that XD).