30-32 seems to give good economy, good tirewear, and good handling. 28 would be low. If you carry lots of heavy things, 33-34 would be better as long as you don't go past the cold tire pressure on the side of the tire.
Depends on the tire too, and always check the tire pressure when the car has sat for at least a few hours and is cold! TP will be higher when the tire are hot.