Part 1 was the best for me.
Mainly the CE Arc was the best. When Gaara was introduced, oh boy my liking for the series went up. Second best villain in Part 1 after Orochimaru. The Chunin Exams showed me each of the char's potential.
Sasuke's ability to copy taijutsu techniques under a month.
Rock Lee's hard work- 5 Gates GG, you should have seen the look on Neji's face when Lee pulled out his trump card against Gaara. The dude was jealous.
Hyuga Style Taijutsu and Neji's intellect to analyze the field. 8 Trigrams 64 Palms, Rotation, Gentle Fist, etc.
Mainly I was impressed by Gaara's liking to kill. I wanted to study his reasoning about why he lives the way he does at the time. I also liked that Neji was a savage, putting people in their place.
Overall up to the conclusion where Orochimaru outlasts the 3rd this arc held the most hype for me. I liked Part 1 because they analyze each character's skill set a lot more. There is no spamming and characters are not that overpowered which makes it fun.