Consumer Reports makes very clear which brands might be keepers:
In years past, there were numerous brands competing in the portable navigator space. Now there are essentially three main players: Garmin, Magellan, and TomTom. All others are truly fringe players and their products should probably be the first to be brought to the return counter. They may well be outdated and future map support may not be convenient.
Then come the details of reasons to upgrade:
lack of traffic, lack of lifetime map upgrades, poor windshield holders
The biggest question:
Is a phone app good enough, especially one from the vendors noted above? Short answer: sometimes, but get a car charger since these apps eat battery power quickly.