There are a myriad of options out there but I'd try to get a "last generation" model with lifetime updates.
I'd only buy Garmin. TomTom is horrific in my experience.
I'd buy based on parameters - the latest ones should have:
Spoken street names (text to speech)
Correct lane identification for complex interchanges (awesome feature)
Flat profile for packing if needed
Lithium ion battery if for some reason disconnected from power
Traffic updates
Under $150 or 200 unless that is not a concern
For RVers, there are also options for truckers that includes height limits in navigation and truck routes.