I'm a Shu fan, myself. Probably because I always like to root for the underdog. Favorite character would be Zhuge Liang. Even though he has become more of a legend than he really was historically, I still enjoy his character and story a lot. Least favorite...hmm, probably Dong Zhuo. I've never been able to use him well.
I have to admit that I lost faith in the series with the fourth and fifth installments, but they won me back with the sixth. They finally made some much needed changes to the core combat and actually made generals a genuine threat now. Seeing three or more generals (even the lesser known ones) coming at you now is something to actually be concerned about for a change.
The regular troops are still just fodder, but there's actually a purpose to that now (using them to get your combo gauge up). Here's hoping they continue advancing the series and don't just make the next several games re-releases of six.
Also, I don't know if I would personally call Cao Cao evil. He was a brilliant leader and, more than being evil, simply did whatever he needed to do to win. I guess you could say that is in and of itself an evil thing, but in war the lines get pretty blurred between good and evil.