I just received my 'Servin It Up' box set yesterday, only fifty bucks for part 1 and 2!
It's really tough choosing which one is better. Part 2 contains more cutting edge stunts, but part 1 shows Darius' stunting progression. Part one also shows off his badass 700 hp V8 240z.
If there is anything negative I can say about 'Servin It Up' part 1, it's that some of the footage I had already seen in Crusty 8 (like when Darius eats shit on the freeway). In Crusty 8 you don't actually see the damage done; 'Servin It Up' shows the reconstruction of Darius.
Overall I can't pick one over the other. My advice would to buy both like I did, that way you have all your bases covered.