I have a Garmin GPSmap 62st. It comes pre-loaded with Canadian topo map. Good reception, even under heavi cover. Big pluss is being rain-proof, and useable with the gloves on. To me, the best feature is being able to mark my location and mark locations baased on co-ordinates.
The map it comes with, well, not so great. When I am off the popular trails, the smaller trails and some part of cutlines and snowmobile trails are not on the map. Most of the time, I was hiking down a trail, that is not on the map. Getting to another trail, that is also not on the map. Creeks and ponds are also missing. So, mostly the map is just a blank page. The good thing is, it marks your tracks on that blank map, so when I zoom out, it gives me a pretty good picture how I got there.
I don't have any experience with other off-road GPS units. Besides the map it comes with not very good, I think it's a good unit. It's good enough to take it with me every time, to go up North and find my way.