Well now that the "corrupt rulers" post is out of the way, the busiest are going to be:
Sheriff Ch 1,2,3 and 4
City PD 1,3,4, and 6
Citrus Heights 1
Elk Grove 1
Fire A2/A3 and B2
Other have a lot of traffic, but won't be interesting. Those are SD 5 (records) and chit-chat channels such as City PD Ch 2 & 5.
Folsom is pretty quiet, generally. Lots of vehicle stops, but that's usually it. Maybe a fight as the bars let out.
Grant is probably a little busier now that they've expanded their facilities.
West Sac is often good for a listen. They often have something happening.