I had a Garmin back in the days when disk based (not flash card) GPS systems were pricey, then it got stolen and I replaced it with Magellan then Tom Tom then went back to Garmin. I tired Magellan and Tom Tom because they had them cheap at Costco and I knew I could take them back. Good job since I hated them. Had to go back to Garmin (360) for a very simple reason - I don't need to be distracted by GPS and Garmin seems to have the cleanest interface and most straightforward map display. If you are driving on a long ride, you want to listen to music and radio not directions. Garmin has a display that I just need to glance at in order to get all the info (next turn, miles/feet to go) and map that shows road ahead in perspective.
Maybe it's just me, but I found all other interfaces and map displays cluttered and annoying.