Steve,
Either will work, but you have to get a mount and car cord for the cell phone. Then, set it up to not blank the screen and remember to download the maps for the days travel.
I never use our phones for that because their routing sucks if you are away from the blue roads and if you did not get the maps loaded, you can end up driving off the end of the world....
I have never seen an app that does bridge clearance, weight limits and propane restrictions. The dedicated RV GPSs can do this.
It all depends on where you are planning to go.
Matt
Matt & Mary Colie
A sailor, his bride and their black dogs (one dear dog is waiting for us at the bridge) going to see some dry places that have Geocaches in a coach made the year we married.