I have the Garmin RV 760LMT which I am very happy with.
I always plan my trips ahead on my computer using the free Garmin
Basecamp software. Most of the time the calculated route is fine but occasionally I will want to tweak it. You can easily see the route on your computer, spot problems and tweak it by inserting waypoints to force it to take the route you want.
As others have stated no GPS will get it right every time, but if you plan out you trip on your computer first you can avoid the surprises. Another thing I like is that it gives me a permanent record of all my trips. I think something like Basecamp is essential and it only takes a few minutes to plan your route.