Bane. For a number of reasons.
1.- With a younger Batman comes a younger Bane. That's the one variable I have yet to see anyone acknowledge.
2.- Bane and Batman had the same training. Bane knew what Batman was going to bring to the table.
3.- Bane was born in the strife that Batman only really got to emulate. This can drive a fighter a lot, as they're born into that fire, rather than attempting to throw themselves into it and expect a similar outcome. Compare two new students in a martial arts class who have just earned their second belts. One grew up in a safe neighborhood, while the other had to fight his way to school every day. The latter has had to learn how to fight to survive, not fight to win a fight. That goes an extremely long way.
4.- Bane is not only physically stronger (which will certainly help in a match versus an equally or more skilled opponent), but also tougher. Not only because of his pain suppressant, but both films make it very clear he can take extreme punishment with little to no damage. Pain slows, but damage stops. Bane didn't take damage, even aside from his pain. Bane very clearly toyed with Batman throughout the entirety of the first encounter they had.
5.- Up until Batman met Bane, he had never had an opponent who could match him physically. All we saw who gave him any semblance of a challenge was Ra's, which wasn't a lot. Just like Batman clearly didn't know how to react during his first fight with Bane, an even younger and more arrogant Batman wouldn't have known what to do in his earlier years.
I still think, had Bane been the villain of one of the first two films- inspiration from Knightfall aside- the outcomes would have been the same. Batman finds an opponent who is bigger, badder, and more dangerous than he's ever seen before. Bane used his own strengths and exploited Batman's biggest weaknesses. One of the greatest of which, up until The Dark Knight Rises, would have been his inability to react appropriately to a larger threat than some jackass with a machine gun.
However, Batman, being as intelligent as he is, would have eventually figured out the mask, I believe. I still stand by him losing the first fight, but returning prepared for the second and winning.