I get asked about this a lot, maybe because I used to wear a name tag that said "Navigator".
Cell phone and particularly Google and Waze are good as long as you have coverage. We travel strange places and even with Verizon Coverage and a 38dB gain repeater, will still loose coverage and that often for 50~100 miles. If you don't get off the beaten path, you don't need more.
We run with three GPS. Not really a geek, but as I am a navigator, old habits die hard. It goes like this:
There is a 2595 on the dash for the driver. It was loaded with the day's route before the main engine started.
There is the Droid in the repeater cradle that will be running either Google Maps and/or Waze (Waze is useless outside of urban areas), and it is also being a hotspot.
The laptop in front of the navigator will be running Street Atlas real time from a GPS puck and GasBuddy (easier on the big screen). SA tells us where to think about fuel and what may be a good place to overnight. SA on the laptop also has the entire excursion plan. All of it, and many of the projected stops. That carefully arranged plan is usually pretty good from departure until noon of the next day. After that, changes are regularly required because we discovered someplace we never knew we wanted to see or some place we had read about, included a several hour stop, and on seeing it decided against even slowing down.
Needless to say, the separate driver and navigator jobs makes travel much more pleasant. Either can do either.
Don't like to have DW drive??? Get over it.
Matt