I'll challenge this and say the uchiha clan will win.
Firstly what you seem to forget is that gedo mazo needs a life source to operate thats why it stabs nagato's back. In tobi's case he had the 7 tailed beasts in it therefore there is more than enough chakra for it to operate.
Now what you fail to get is that a healthy itachi alone can compete with a healthy nagato although itachi would most likely lose. Not sure though because raw power obviously goes to nagato but speed, skill and intelligence goes to itachi.
Now the uchiha are said to be a clan of geniuses. Anybody who says itachi killed them all by himself therefore nagato can are fools. Not only did itachi not kill them by himself but also there was an element of surprise. Why do you think he did it at night.
What i would say is that deva realm would pose the main problems because as weve seem the other paths arent as strong. 3 people from kiba's clan couldve defeated hungry ghost realm. Also kakashi, choji and choza nearly got the better of deva real until asura path came to the rescue