You may want to include both for all around shoulder development (at least front and lateral heads). Military presses will target the anterior head and the lateral head to a lesser degree. DB presses (depending on how the hands are placed for the most part) will target the lateral head and the anterior head to a lesser degree. DB's will also insure an equal amount of balanced development and strength. Most people will favor one side over the other with a BB, though they may no be aware of it. DB's give an equal work load to each side.
If you want a all around pressing-pulling delt workout, than might try doing the military press and up-right rows in training. Exchange DB's for both or either exercises if you wish, for the sake of variety. Good luck.