closed is best. if the boxes are kept in the humidor/ winedor/ stogie friendly environment, they themselves absorb humidity. keeping them closed actually helps shield the smokes from fluctuations in RH from opening and closing, ESPECIALLY if it is your main, and not a reserve stash to be opened periodically to refill desktop humis.
if you are looking to keep for years, sealed is even better: SLOW air exchange is the best for gradual mellowing and development of flavors.
then again, if you need to see your stash, and can keep a stable RH, keep them open to look. o)