The city and local club have done some excellent work on Knox. I used to live at the base and it always made for a great couple laps.
I would recommend a few rides on the mountain if your in town anyway, finish off with a spin out Paul's Tomb and a quick dip in the lake. A shuttle would take longer to get down than riding down but a great way to get a bunch of laps in quickly.
Smith Creek is a must hit for everyone in my opinion, it is worth the trip across the bridge. Crawford is great but I don't like it in the summer as it is wide open in the sun for lots of the climb up, better in spring and fall.