Tough choice
Chunin exams are what got me hooked
The mini arc with Jiraiya in amegakure was fantastic (anime)
Pain arc is also top 3 I was speechless when he just destroyed the entire village. The only reason this isn't my favorite was the whole Naruto talking pain to death and him reviving everyone. The show would have been better if Hinata died. (So people can stop arguing over pairing.)
But the winner is:
Sound 5 arc. I remember in 6th grade my friend told me that some of the rookies were going on a A rank mission and I was so excited. Seeing the K5 (Kiba, naruto, neji, shika, choji) standing in front of the leaf village still gives me goosebumps. Those were my favorite rookies (except choji, he sucks) and they got to show off their new techs and get some character development. And it ended on a high note with Naruto vs Sasuke. The only thing that could have improved this arc is if they replaced Choji with Shino.
