Personally Orochimaru would win. And here's why:
It is implied that Jirayai was more powerful in his youth than later years. While the Toad Sage traveled the world, writing novels and gathering information about Akatsuki,he probably got weaker with age. Orochimaru actually got better. He was doing experiments on himself to get a better body. He also learned lots of jutsu along the way.
Even though Itachi easily defeats Orochimaru with Genjutsu, this was a Orochimaru almost 12 years before Naruto. Orochimaru had gotten better by then.
Itachi states to Kisame that if the two of them fight Jirayai they will lose. I'm guessing Itachi is going by Youth Jiryai's reputation as a Sannin. In fact without Sage Mode Jirayai would probably lose to Itachi and Kisame.
Orochimaru did way better in battle against the 4 Tails Form than Jirayai did. Jirayai was inflicted a large scar on his chest prior to fighting 4 Tails. But Orochimaru doesn't suffer any major injuries fighting against 4 Tails. You can put into account that this is because Orochimaru's regenerative Abilites, able to relatch and dispatch of his body at will. Still nevertheless, this orochimaru is sick not healthy. Therefore the one fighting 4 Tails is not at full power, yet he is able to put up more of a fight than a healthy Jirayai. So 4 Tails > Orochimaru > Orochimaru(sick) > Jirayai
