Why?

Well for starters I prefere Nod infantry over GDI's any day. The Chaingun laser black hands easily rip up enemy armor and infantry. And while Gunner deals a good amount of damage too. I like instant-impact weapons over the rockets which give enemy units time to manuver out of the way.

Moreover those Cloaked black hands really come in handly. Great for taking out those pesty snipers with a laser headshot or sneaking behind enemy defense to plant a nuke or something '...never know what hit them'

You might say that GDI armor is better then Nod. But I have never seen 4 Medium tanks successfully rush an Obelisk before. Whereas flame rushes are so popular an known nowadays all I have to do is ask 'who wants to flame rush?' at the beginning of the game and already I got like 3 to 4 volunteers who would be glad to flame rush with me once we got the cash.

Another sad thing the AGT. Nod not only has an Obelisk but 2 Turrets. While GDI has a cheap a single AGT that can't do crap against APCs much less flame tank rushes. Good against infantry yes. But how often do you see swarms of enemy infantry rushing against the base hmm?

Mammoth tanks are laughable in Renegade. A couple of blackhands and the Mammoths are already forced to pull back. Even when they successfully gather 4 ~ 5 mammoths to rush the Nod base they usually fail. They're big;choke up in maps like field or hourglass(if you take the sideways), slow; the obelisk gets to fire probably once or twice before they even return fire. And expensive; when mammoths rush 1 or 2 does the rushing.. everyone else is too scared to move in afraid they'll lose their oh so valuable tank.

I ain't saying Nod is invincible, but these are the advantages I see in Nod over GDI.

And Nod have a way more charismatic people on their team. Who leads the brotherhood? Kane. Who does GDI have hmm? That forgetable weeny General Whatshisname from C&C1?

Michael Bien in C&C:TS was okay, but compare him to Slavik (Bad ass 007 villian type)? Please... not to mention Slavik's got that really hot babe of a Lieut...

Even their command AI was cooler! GDI's no frills EVA.
EVA 'Stand by for battle control'
While Nod had :
Cabal 'Reaching the base will increase chances of a favourable outcome...'
Slavik 'Cabal Define favorable outcome...'
Cabal '...They all die...'