I haven't purchased a GPS in a number of years, and I'm sure there are more capabilities now then when I bought mine. That said...
Without an idea of what sort of features are important to you, it is hard to make a recommendation. Sort of like when someone asks you "What is the best gun to buy?"
A car-mounted GPS can't be removed from your car to carry around, while a handheld GPS can be mounted in your car with a bracket. The newer handheld units can easily be used for car navigation as well as hiking, while the car-mounted models are going to have very car-specific features. For example, bigger screens with more 3D-like views.
I would suggest that if you are even asking the question, you should probably go with a handheld unit. You might not have the option of a pleasant voice saying "Turn Left" while peering at a pretty 3D-forward-looking representation of the freeway offramp you just took, but it will sure get you where you need to go both in your car and once at your destination.
And yes, last I checked, Garmin is the route to go. I have an old Garmin.
-Caver