All bases fly all of the airplanes. Typically, the lines are built as 200 lines and 700/900 lines, but once you hold a line, you can easily drop/add trips so you will likely have a mix. If you are DAY or TYS based, expect to fly the 200 more than the 900. If you are CLT, you can go 6 months without flying the 200 unless you try to get it.

Personally, I have flown all 3 types on the same day on several occasions. It happens.