Naruto is the only one i beleive that can beat Madara. If Naruto learns to control the Kyuubi he can do a complete transformation and without side effects more then likely, also the Kyuubi is the strongest being in the Narutoverse, he was controlled by madara by an extremely powerful genjutsu seeing as that is the sharingans special ability. Remember the way to break a genjutsu is to disrupt chakra flow, ergo the fox backs-up Naruto and vice-versa. Also the fox's cloak will help Naruto from being hurt. Naruto will also gain a tremendous amount of stamina and chakra ontop of what he already has. In my opinion i think it will basically come down to a chakra battle, whoever has the most will be the last one standing, I beleive this because Naruto already has a large chakra reserve and if he controls the Kyuubi it will be evn greater. The control of the Kyuubi will also allow him to sync with the frogs which i doubt he will need but it is still a posibilty. He could possibly mix the two chakras and gain immense almost god0like power. So in conclusion this is why Naruto will be the one to defeat Madara