Here's the problem I had with SC1. Mitsarugi was WAY overpowered. His "pick you off the ground sweep" and keep doing over, and over again was shit.
They minimized that in SC2. Both have thier problems, but SC2 has less, and more importantly less game ruining ones.
Most of the charactors are balanced in SC2, and the graphics are 2x better ta' boot.
SC2 all the way.
(I write my opinions becuase me and my brother had ALOT, and most of the time VIOLENT marathons of SC1, and 2, and he used Mitsarugi, and I used Cervantes. We both came to the conclusion that SC2 is the more balanced of the two. We played a ton of matches of both, using the same charactors just to see, and without a shadow of a doubt, SC2 is the better, more balanced fighter)