Madara, with moderate difficulty.
Without Gedo Mazo there's no way for Nagato to actually hurt Madara inside his perfect Susanoo. And I can hardly see it falling prey to Chibaku Tensei, considering that a mere swung of its sword, without actually touching anything, destroyed an entire meteorite and cut two distant mountains. And as if that's not enough, Susanoo can wield two of those huge blades.
The rest of Nagato's summonings won't stand much of a chance before Susanoo's sword and Amaterasu.
As for absorbing Susanoo, that's nearly impossible. That thing has about the size of Gedo Mazo, meaning that even one of its fingers has at least twice the size of Nagato. He took a few seconds, not an instant, to absorb Bee's human-sized Bijuu cloak. If he tries to absorb Susanoo, it'll just kick him away or directly attack him with its swords. That is to say if he actually gets close enough. Susanoo is, despite its size, not in any way clumsy. Quite the contray, it's very fast and agile. Somebody claimed that absorbing a tiny part of Susanoo would 'destabilize' it, but that's completely made up out of thin air, considering that not even the rotation Jiraiya's Chou Oodama Rasengan became astable while being absorbed. Furthermore that stabilization seems to be nothing but Susanoo obtaining its armour. But even if parts should be absorbed, since it's made up of Chakra, it can simply regenerate. Most importantly, Madara can still act while being inside it, probably even leave it.
Now, I didn't even mention Madara's Genjutsu or his giant fan, that is currently under Tobi's possession and whose abilities are yet unkown. But since is Tobi's carrying it around all the time, it must be pretty delicious.