DOT 4 or DOT 5.1 (do not even begin to think about DOT 5--it is incompatable with Dot 4 and DOT 5.1) I use ATE SuperBlue/Gold, 2-3 complete flushes per year, maybe more depending on track use.
ate superblue/gold for me too...it's easy to flush and know your doing it complete when changing from blue to gold then gold to blue