My dad taught me when I was little to always keep both eyes open, so thats the way Ive been doing it since I was about 6 years old. I have to agree with those that said it is more relaxing to keep both open. It gives a much more natural feel.
I have been shooting with both eyes open for as long as I can remember. In my adolescents, I was enrolled in cadets where they had a shooting range. My first time there, the range officer noticed I was shooting with both eyes open and proceeded to yelling that I was doing it wrong and should have one eye closed.
After "hearing him out" I tried with one eye closed and couldn't hit the side of a barn for the life of me... more screaming and yelling followed. This guy was a knob... a complete *****!
Once he was done, I went back to both eyes open only to hear him praise me for the terrific shooting. Proudly, I yelled, "That was with both eyes open! Wanna see me try again with one eye???" Needless to say, he shut up rather quickly and to this day, I still shoot with both eyes open. It's just habit... not comfort or any other reason.
Handgun, shotgun, bow, both eyes open. Rifle, depends on light conditions but there is no difference in accuracy either way. Both open gives faster target acquisition. I have found that regulating my other eye can control the image clarity with glare or low light. IMO.
"Let us speak courteously, deal fairly, and keep ourselves armed and ready"-T. Roosevelt
I keep one eye closed with rifle, I'm right handed and left eye dominant, bow I keep both open but, I shoot a bow left handed. Pistol I keep right eye closed but still shoot right handed, though I could keep them both closed and do just about as well, I suck with a hand gun