Look

All we know for sure, is that Orochimaru said that Itachi was stronger than he was. So we can assume in a one on one fight Itachi would beat Orochimaru. Orochimaru's main thing is techniques, Itachi probably knows a lot more than him and most likely counters for most of his techniques.

Jiraiya was able to beat back Itachi and Kisame, but that was under some special circumstances. Itachi and Kisame both fought like the day before, or maybe even the same day. Jiraiya was fresh and ready to go. Not that I don't think Jiraiya could take Itachi, I believe he could, but it just hasn't been proven yet.

Tsunade...well, we haven't seen her in action enough yet to know for sure. She has shown us that she is quite talented in the medical jutsu area, but other than a summoning, we haven't seen much of her other ninja techniques. Physically she is a freak, so her Taijutsu is probably good.

Just until they actually fight, we don't know for sure, as in Naruto strength doesn't necesarrily mean a win.