First, the obvious big differences:
Garmin does not have and OSK (mine does but I had to code one into the FE for it)
Odyssey and Navigator free both have an OSK (on screen keyboard.) Odyssey has IMHO the best OSK, it’s really nice to use and the OSK interface to the application search if so easy.
IMHO again, Odyssey is the easiest program to use on a small screen, Garmin next then Navigator11, Nav11 feels awkward and in some cases frustrating to use. I think Odyssey edges out Garmin with its turn previews and clean layout. It’s definitely the choice for inputting a new address and changing or adding to the route quickly.
Picture of a location at a close zoom level. Zoom levels are finer on Garmin and it’s hard to match each GPS app as they skip to different views but here goes. (Garmin set to least detail).