For SX...I would have to say Motoland in Casa Grande, Az.  so far is the best training track.  This place also has a mx track and beginner track, and is operated by some pretty nice people.  They really make you feel welcome, and will do anything they can to help you out.  If you are in the area, it is definitely worth checking out.  The SX track is only opened to AMA pros...unless otherwise prearranged with Chip.

Looking back on all the tracks, I would have to rank Albany MX one of the top tracks that I have experienced.  It's not so much the condition of the track, you know like dirt, sand, hardpack, etc., it's the fact that they can change it so many ways.  I rode that track for a straight week and never rode the same layout twice....it was off the chain.....I was told that they have something like 28 different layouts.

The best kept secret in So-Cal is Cal City MX Park.  CCMX is a great track.  The owner, John, has done an excellent job on building a challenge.  I guess some racers have shown up, but left because it was to hard.  I say bring it on.  It's about time serious racers have a real track to practice and train.  Right now they are open Thursday, Friday, Saturday and Sundays. Check them out at CalCityMXPark.com

In Northern California I would have to say that E-Street is the best work out track for training.  With the sandy conditions, it really makes you step up your training program so you can last 8 laps in a race.  Do a couple of hard 30 minute motos each practice and you will definitely kick it up at race time.   Also, for a small tight technical track, Ukiah Speedway has really stepped up thier layout.  Ukiah is North of Santa Rosa off the 101, it is definitely worth the trip.