I use three different GPS systems... one on my phone (Goggle maps), one in my Hyundai SUV (2017 Santa Fe), one in my Sling... the three of them never agree!
Hyundai offers the most options - avoid tolls, ferrys, etc - and these actually work. Fastest time, scenic route, etc - as long as you know how to set the preferences, you are okay. Easy to use, but often can't find addresses if they were added in the last 15 years or so. It's GREAT on highways, guides you to the correct off ramp every time, navigates through cities with ease.
Goggle lies, lies, lies - and if I express a preference - it says: "F-You!" and changes the route anyway - then it nags, nags, nags "Turn around! You're going the wrong way!" (It's like driving with my mother tanked on meds!) It is the easiest of the bunch to use and the only one with a functional voice command. (Hyundai voice command is like speaking to a partially deaf autistic person who didn't grow up speaking English...) Goggle is also easy to add way points. Terrible in cities - sure to get you lost or take you off into a hell-neighborhood 'cause it's faster'. Does keep up with road closures, traffic, cop traps.
The sling doesn't offer options, nags less than the others, is harder to use. Still, it is on screen and uses a bigger screen than my phone - but text telling you what road your on is TOO SMALL to read, even in ideal lighting - makes you wonder if you need new bifocals all the time. Does okay in cities, not so much in the country. "Hey! You know that gravel road that goes through a swamp? You GOTTA take that! It'll save time! TURN NOW! Wait - GO BACK!"
Ugh! I really prefer to know where I'm going than rely on technology!