I have been to almost every track in This region and my favorite is Moto City Race Park. The day track is like an outdoor national. It is sand but it isn't to deep. It's the best dirt ever. They have a night track there that is really good too. It gets really rutted on it and is good practice.
Watch out if it rains a lot there cause the sand turns to quicksand. I got stuck out there when I practiced there last time, but the dirt is perfect.