its whatever works best for you man.i shoot better with both open. like stated above, i am right eye dominant and have good eyesight so my right eye takes over. if i shoot with my left closed its way harder (for me) to be consistant. now i gurantee you though, if i practiced on shooting with one eye closed and forced it i could shoot well like that. but its really all about whats comfortable. find out what u like and stick with it. dont go listening to your buddies or anyone if they tell u one way is better than the other. good luck
Derek