I guess GPS hiking dedicated devices users love Garmin and probably would like Garmin for automotive use too, especially North American users.
In Europe for cars a lot of users like TomTom.
Phones users like iGO especially the ones who likes to mod the apps a bit iGO is a very good program and can play with it.
Users who doesn't want to have hurdles and problems like Sygic: easy
Users who want free maps and free app, like Locus, Orux and Osmand: all free, app&maps, but OSM maps quality is lower.