i think sound is better.

a. your car will never look good enough if you go the ricer way

b. your car will never be fast enough if you go the mod way.

c. if you upgrade sound, you wont waste incredible amounts of money (unless you going to shows, and if you got neither show or go.. then forget about it). And in the end you can always put taht sound system in another car, rather then loosing all your money in go or show parts...