I wouldn't use Muscle Milk post workout, but thats just me. Personally I use it 2 times a day. When I am bulking, I will use it as my pre-workout meal, and then I have another shake before bed. In my opinion, it is one of the best shakes to drink at bedtime.
When cutting, I drink a shake around mid-day, and again at nightime. The good fats in Muscle Milk are again perfect for cutting, and are great for nightime use.
The best ones in my opinion are:
Rootbeer Float
Blueberrys and Cream
Cookies and Cream