I have found that we need a mix to be effective. The thing a smartphone is great at is
with that and Gasbuddy, you can reduce the effort of travel greatly - as long as you are in an area where coverage is good. We tried to go with just a smartphone (Android), but that not great for planning because of the screen size and limited information. We are also not "Blue Roads" people. This caused us to frequently be off the edge of the map data. Even if you pre-load the map data for where you think you will be, this does not always work as planned.
On the bridge of out coach, we have a standalone up to date GPS with the most recent updates. That gets loaded with the day's plan before we even get underway. This one has the traffic service, and it is pretty good, but not great. It does have the advantage of never driving off the edge of the world.
The standalone is a Garmin and routing they provide is way less than ideal for us. Google maps is even worse. Street Atlas that is running on the navigator's laptop is far the best for this because you can see the entire route in detail as soon as it plots. The big problem there is that the chart data is now five years out of date and there is no update available. The smartphone is also being an access point when needed, but even with a high repeater and a high mounted antenna we frequently totally out of bars.
I have been trying to change routing to Furkot for planning and as it is an online thing, trying to use it for navigation underway is at best problematic. I have also have no success getting either it or Google maps to read from a USB GPS realtime.
The loss of SA and the tables of waypoints (POI) is a vast inconvenience. I marvel that the technology has gotten so far along that I often have to go back to my paper charts. I am distressed that Garmin killed it without a replacement. And no, the Garmin computer apps are terrible and problematic at best.
Matt