Peep by far is my choice but since it's not on the list I would take a square over V a million times in a row. If it has a V I am changing it. I've shot both and a V is not as precise as a square, I need to see light on both sides of the blade through the rear sight and the more vertical space I can see through the better chance I have of getting a well centered blade. For this reason I prefer sights on the tall side to almost ridiculously tall. This is even more important in field conditions and in poor lighting conditions, the more vertical real estate you have on the sides of the blade the better chance you have of seeing at least contrast to get it centered, first light or last light it is crucial for me to be able to shoot to my best ability. Flat top is also required for me, you will register the top of the blade level with the top of the rear far easier using a flat rear and a flat blade than any other combination.