If you could pick two ninja throughout the anime to fight, who would it be? why did you pick them? who would win?

If I would choose two ninja, I'd choose Neji vs. Gaara. Gaara would win because of his demon. Neji might block off gaara's chakra, but not Shakukas.

Zabuza and Gai would be a good fight.

well if neji and garra fought neji wouldn't be able to get to garra cuz hes a long range fighter when neji is close range

That's also true.