Damn, tough question, especially since there are so many combinations. I will say that I HATE the new DA, and McCoy's new assistant. Both of them are horrible actors, and they get on my nervers. Schiff was a GREAT actor for that role. McCoy and Stone are both good, but I tend to like McCoy's speeches more. The Three Brunettes

were all great, much better than that new blonde chick. Ugh. As for the officers, Brisco is awesome, Curtis is a good character, Logan is an a*shole!, and I can't remember the names of the other guys. I don't like the blonde guy, but I do like the big dark haired guy with the fat nose.
It's good that they were able to change casts so many times and still keep the audience. They really know how to write each character so that you like them for themselves, and not comparing them to the previous guy.