What method yields best result for washing breads?
I have always used egg and milk. Two thirds egg to one third milk. Use a spray bottle to ensure that you get a nice, even coverage.

Also make sure that you have a full proof on your goods, because (obviously) anything that gets exposed to the heat due to oven spring will not have color.

Just the way I have always done things (and I used to work in some pretty nice pastry shops back in the day).

EDIT:

Just noticed the comment from sour d'oh... Should've mentiontioned that stuff myself... Very important. The higher the fat of the dairy, the better the color (use a high fat cream instead of milk).