Sling, no contest. From the moment I pull it out of the truck, I open the action and put that thing on my back for the boat ride until we get to the blind. Exception being if it's raining or snowing but as you know, that's few and far between here.
Real advantage of a sling is after the hunt--gun gets air dried and doesn't have a chance to fester in a case. Just obviously be sure to unload it and open the action so those around you can see it's unloaded.
The other advantage is when I have to go out into the spread during the hunt to switch batteries, etc. Put the gun on my back because you KNOW birds will come in when you least want them to--especially when you're switching stuff up because they haven't been coming all morning!