It seemed to me that Nagato was much more powerful without the use of the Pain/Pein.
(This thread is made assuming that Pain/Pein is NOT being controlled by Nagato)
I have been going through threads and I believe that a lot of the community seriously underestimates Minato, personally I think that Minato would have a good chance at beating Itachi, though I don't know how he would do against Genjutsu.