MK9 and Armageddon.
MKA had the biggest roster so there's that.
MK9 is simply objectively the best because of how safe it was. You absolutely can't go wrong by choosing characters everyone likes already. Fan favorites are ALWAYS gonna be safer and more popular as a roster than new characters, because even if 3/4 of the new characters are awesome there's always gonna be garbage in the middle, that's just how making new characters works. Especially if the majority of your community grew up with the classic games, even if some characters happen to suck absolute ass people will still love them because nostalgia is a hell of a drug.