Hmm, It'd be a closer fight than a lot of you think..
Bijuu's will fire off TBB's like it's no ones business, and Nagato can absorb an unlimited amount of chakra via Preta path, so these TBB's will do nothing but aid him.
Both could use Gedo Mazo, and we haven't been told which one can, so I think we should rule Gedo out. People will say that because when Nagato last used (we last saw) Gedo Mazo, it left him looking thinner and ill, this is because of the sheer amount of chakra that Gedo requires. TBB will give him more than enough chakra to operate Gedo without the use of his own chakra, so for this reason, I believe Gedo would not penalise either fighter, and so should be ruled out.
So, if Tobi's paths don't use their beast form and attack normally, it's fair to say that Nagato will destroy them, as he knows about the shared vision and the paths ins and out, and if they decide to use Chakra cloaks, again when they get close Preta will snatch it all up.
It basically comes down to Nagato himself vs Tobi himself, this is a real close one.
If Nagato uses Chibaku tensei, Tobi will either go intangible or the Bijuu's will break if for him. Tobi's intangibility plays a massive part as Shinra tensei can't really effect him, and the big problem for Nagato is Tobi's s/t. When I say his s/t, I mean what did against Minato, when he tried to somewhat 'absorb' him, or send him to the different dimension. This does seem to be somewhat of a precise attack, as he doesn't use it on moving opponents, but it is a fast jutsu. It comes down to whether Nagato can Shinra Tensei him before he absorbs him. This is sheer speculation to say Nagato can shinra before Tobi s/t's, so for this, I think the win goes to Tobi.
