I purchased the Garmin GPSMap 60c this fall along with the Topo map package and I love it!!! Make sure to get a unit with an external antennae, so it will work in heavy tree canopy areas.
The unit shows most two tracks with a fairly high degree of accuracy....of course no unit will show every woods trail (due to constant logging which leads to trails changing all the time.
The snowmobile trails are NOT marked as such, but they also tend to vary from year to year.
Some units go thru batteries like crazy, but I have been using mine for a couple of months and still on the first set of batteries.