Well if you want to see as much as you can of the zoo pick a weekday since it will be less busy. When you get there start with the Pandas if you want to see them, the line will just get longer the longer you wait in the day.I'm sure there's really no *great* day since it's a pretty long drive. We are planning on staying in Anaheim Sat to Sat, and we're pretty open to what day we go to the zoo.