In this scenario, i thought about doing a rinnegan vs rinnegan. This fight is obviously impossible to have happened at any point in the story, since both of them share the same eyes practically, but let's do it anyway. Nagato is redheaded, can use his legs, and pretty much is the one who fought Naruto, Bee, and Itachi after taking Bee's chakra. Madara is the one from the war, he also has both rinnegans. He doesn't have Hashirama's SM, but he does obviously have his cells.
Restrictions: They both can only use rinnegan abilities that they already displayed in battle. Meaning that Madara can't just randomly pull a shinra tensei or anything like that. Madara is also restricted from using any version of Susanoo above the one he used when he got first reanimated. So pretty much he can't use any version of the Susanoo that has legs,because let's face it, it's not really a debate otherwise.
Nagato only knows about Madara's abilities from stories and legends, and Madara only knows about Nagato's rinnegan.
They fight in an opened field.