It would definely be tsunade for me. not only is she stronger than orochimaru and jaraiya (physically) she is super hot! xd. plus she outlive them all! xd
Anyways, my favorite villain in whole series is Orochimaru but I still say Jiraiya.
I consider Jiraiya as the strongest though in terms of liking, both are great and creative characters.
As much as I love Jiraiya (he is one of my favourites), I would have to go with Tsunade because her personality is BAD ASS - which is seriously like mine... goes in there and doesn't leave until she is finished.
you can argue that jiraiya does that too... damn this is hard.