Kind of hard to chose when they really aren't even that related! Chitala evolved the shape first (and same with the asian and african Knifes), but Gymnos have the EOD organ. What about mormyrids (african electric fish)? Some of those species other than the typical elephant nose are knife shaped too (i.e. Abu Abu knifefish).
Chitala Ornata was the first Monster Fish that I saw when I was 6 years old. Fell in love with the hobby ever since. I currently have a BGK and CK. Both are pretty different, but because of my first sight of a Monster Fish, Chitala for me