I just recently switched to a Garmin Nuvi from a Garmin Quest. I've owned various Garmin receivers over the last 12 years or so and have always been happy with them (except for the eTrex series, but that's another story). That said, I like the Quest much better than the Nuvi. Sure, the Nuvi has a large touchscreen and a pretty interface, but the Quest has a lot more features and I think is a lot easier to use. (Of course, it cost twice as much too).
As far as using a smartphone as a navigation device: it's great in that you always have it with you, and I have used mine a few times (usually as a passenger in somebody else's car), but I just don't think it's as easy to use as a dedicated GPS receiver.
Also, in Columbus, Ohio (and various other places, I'm sure), "sending, reading or writing a text message or accessing the internet while driving" is now illegal. As the law is written, it is legal to use a standalone GPS receiver, but it is illegal to use your smartphone for navigation.