For me, I'd choose a daysack every time. Apart from the ballance/swinging about issue, I reckon that if you're stopping to get something from you haversack, you're going to pause - however briefly - anyway and have a break from your wanderings. Taking off your daysack in that time requires no more effort and energy. I tried a 'shoulder bag thing', albeit sceptically, and found it to be a real pain: always in the wrong place, never quite able to hold enough, uncomfortable when filled/overfilled and the flap just getting in the way and making access to the actual bag difficult. I do like the retro look though and can see their value as a bag for foraging or gathering kindling and so on once camp has been established. But for a day's walk? I think not.
