Part 1 for me
Part 2 dragged on too long, just long enough for characters to get DBZ like power boost to the point that ninja that were considered elite like Zabuza are total fodder in comparison now; totally dissing on what was great in Part 1
Part 1 just seemed more epic, a little more real. Kakashi was still the man. Itachi was lord and total b.a. There seemed like so much potential with the Neji character. More mystery.
Back in Part 1 the Sharingan was just a little better than the Byakugan and there could be lively debates about which was better; before the Sharingan got totally hauxed with the ability to evolve to other more powerful forms
The fights in Part 1 also seemed more about skill and technique rather than who the most explosive one-shot tech