Depends on how you are going to carry them for one thing. However, if you use 4 small fly boxes you can have more small fly boxes at home, loaded up with particular flies for specific waters, then all you do is exchange boxes before you head out. If you switch to 2 large boxes you will either be hauling around lots of flies that you would never use on a particular piece of water or you will have to be taking out flies at home and loading different flies for that water.

I perfer a number of smaller boxes set up for specific waters.

Larry ---sagefisher---