I have a Garmin Zumo 665 with lifetime maps for use on my BMW R1200RT and the KTM690.  I've ridden through some very rocky terrain with it and it keeps working.  It will show all the trails available on the maps.  Some regions have specific maps with better detail I've been told.  I just use the lifetime ones and Basecamp for planning.  Basecamp has gone through many changes since I first decided to learn it.  I like it.  Others hate it with a passion. No matter what GPS you get you can't beat a detailed paper map to assist you in the field.  I especially like to collect tracks of rides and see where I've been.  I hear that the Montana allows topo maps and maybe a few other functions that the Zumo does not.  The Zump 350 series has a great screen for bright sunlight.