Which side of aluminum foil should face out?

According to America's Test Kitchen, the overall quality of cooking isn't affected by which side of the foil comes in contact with the food. However, Real Simple suggests the use of a non-stick spray on the foil, because most foil sticks to the food unless it is greased.

America's Test Kitchen conducted an experiment in which two manicotti were baked in identical conditions with the exception of which side of the foil they touched. A difference was expected in the amount of browning on the cooked manicotti, however, it found that the foil side had no effect on the finished product.