I always use grid ref because you can easily and accurately reference it to your map and as almost everyone navigating on land in this country are using, or have access to, grid then there is no problem when it comes to interfacing with others, not that I've ever met any others in the places I end up.
I am in two minds about the map and compass thing -mmmmmm It is the only thing that doesnt go wrong I always carry two maps (if you've never had one blow away you aren't trying hard enough) and two compasses but you say you carry two maps and compasses, why if your in two minds about them ??? when walking alone in remote areas but I have also been using handheld GPS since long before SA was turned off and have never had it fail me once. In the cold, wind etc. it is easy to make a mistake with the map whereas it is simple to hold the GPS in your hand and let it put a big "you are here" marker on a moving map display so I might argue that navigating off the GPS, especially in less than ideal conditions, is both safer and more accurate than using the map.