Mage, due to the fact that they differ from one GM/story to an another, with them never being the same. This leads to them being the least generic out of the three, as rogues are quite obvious, same for fighters... Though I guess it depends on what fighters we are talking about, generic small warships in sci-fi that are called fighters or the class in generic fantasy games.
Sure, my mind is unable to comprehend the mages so I tend to stick to paladins, blackguards and fighters when I play DnD and such.
Ps. I am sorry if I used the word 'generic' too often.