Some say SSFII Turbo Akuma or especially Shin Akuma.
But these three pro gamers or cyberathletes are known for being at champion level on newer games than older ones they failed at. Sorry, no subtitles, but actions speak louder than words here:
For me it was Parace l'sia from Arcana Heart 3
Me HAHA! Just kidding... Whilst I have some prowess in Tekken and the original mortal Kombat games I always lose when I go up against someone who is truly skilled. I guess some people have to be the losers in life lol...
Anyway thanks for listening,