We bought a Garmin 660 late last year. We like its larger screen. It has blutooth and I've used it once or twice with my cell phone. It has MP3 player, memory card slot and can play back through truck radio. A bit tinnie sounding We don't use this feature.
We like getting voice notification of upcoming turns and to keep right or left when several lanes split off. This has made travel much easier on the two in cab navigators.
It has a several modes for type of vehicle you're driving. It will recommend different routes based on which vehicle type you select. We set it to "Truck" when towing and "Automobile" when not towing.
We have had occasions when it thinks there is no road yet there is an established one. It is not up to date on some local businesses. This is probably the case with any system that has data stored on the system. I've not checked into how frequently updates are available.
Bottom line - we feel you still need to use sommon sense and have a feel for where you are going. Looking at a map before traveling is still a good way to orient yourself before accepting what the GPS tells you.