Itachi wins hands down. The only reason he lost is because he was sick and protecting Sasuke. Itachi in his prime would destroy Sasuke easily.
I feel that Itachi would have won, all fondness aside, because at that particular time he was still stronger and more capable than Sasuke. Itachi felt that he really wasn't necessary anymore and didn't want to harm his little brother. I also believe that Itachi wanted to die, he was prepared to.