I would do both - sort of
My plans this winter are to add two quality, weather resistant speakers in the cockpit and two down below. Your stereo should have a fader control.We camp in our slip on weekends. I'm looking to be able to plug our portable DVD player or ipod into the head unit as well.Surface mounted speakers will keep you from having to make huge holes in the 'glass but they take up more space. I've seen surface mount types attached to the stern rail.