Part 1. I liked the fights better, the background music really made me bop my head, and there were more diverse theme. Part 2 in a nutshell is all about 'peace peace peace'.
That, and the nine tails transformations in part 2 are insane... I remember in part 1 he barely ever went into it, and I got that sudden rush of evergy every time he did. It's a lot less rare in part 2.