We have both Magellan and Garmin, and the family agrees that the Garmin is just easier to use... the Magellan just seems "clunky", if that makes any sense.
I don't have a "trucker" gps. As many other posters say, use your head while traveling, don't put all your trust in the gps. Gps units especially seem to love directing you to parkways, which many times (around me at least) do not allow trailers or large vehicles.
I usually print out a map using Yahoo maps (which I am used to), bring a large map book, and use the gps while towing. What I really love about the gps is that it warns you of upcoming turns, intersections, etc.
I wouldn't be surprised if dedicated gps unit sort of fade away in the next few years. Everyone is using smartphone with gps, and when we bought our most recent gps last summer we were surprised at how fewer units seemed to be available compared to just a few years ago.
And almost always before leaving on a long trip... I ask here on Open Roads if anyone has up to date info about my route.