I prefer built-in GPS, reason being:
* Location on the map and distance to turns is represented far more accurately
* Knows which way I am pointed and can give accurate directions as soon as I start navigation, while sometimes with my phone I need to move a bit for it to know which way I’m oriented
* Works in tunnels
* Tends to stick to main roads while Apple and Google maps are far too aggressive sending me down side roads or crossing over 2 lanes of traffic.
* Don’t need to pause navigation or mess around with my phone when getting in and out of the car for breaks
* Has detailed information about the services/stores/restaurants available at each rest stop along the highway, and distances to each stop
* Detailed information about lane closures, temporary speed limit reductions due to weather, chain restrictions, etc
* Displays accurate representations of street signs and 3d renderings of off ramps
* Displays landmarks at intersections (e.g. turn right before the ramen shop on the right)
* Shows guidance about which lane to be for two or three upcoming intersections at a time (as opposed to just the next intersection).
* Much more customizable interface. I can choose whether I want it to display gas stations, convenience stores, parking, etc. on the map. How many prompts before a turn. I can enable or disable various features like split-screen turn guidance, etc.
And this is Toyota. Not the prettiest UI in the world but extremely functional. Google Maps is better when searching for businesses and other points of interest, but when it comes to actual navigation I much prefer my car's built-in GPS.