I have both a Garmin Nuvi for the windshield, a Google smartphone, as well as a Garmin built into my new truck.
I like the Nuvi, because you can take it inside and play with it while planning a trip. My nuvi is seven years old and still gets free map updates from Garmin.
On the smartphone GOOgle used to let you plan a trip and save it on your account using a laptop, and then pull that up on the smartphone, but that feature is gone now. I've found traffic is most accurate on the smartphone, because it is real time over the internet from the government, rather than updated periodically by radio station downloads (thats how the stand-alone gps get their traffic.)
The Garmin in my truck is handy because of the huge 8.4" display. The voice recognition feature is awful, so you have to pull over and park to change destinations or search for something... the nanny state won't let you use the keypad while driving. It uses the Internet to find things, which is a feature that costs extra - when my trial runs out, I don't think I will renew that feature.