Never ridden STP, but I live in Tacoma and have been on the road at the same time as the ride and what a zoo. Not a ride I would like to do. If you have a chance, Hurricane Ridge is definitely worth it, 19 1/2 mile climb with 5200 ft. elevation gain and incredible scenery.
Here is a good website with lots of different routes:
http://permanents.seattlerando.org/
Good luck and have fun!