Would you trust any of them for lane guidance? Today we came home with Tom Tom and within a mile of home it suddenly said, completely in error, to turn left. They are not always reliable.
Lane guidance is very hit and miss. It often tells you to keep right on motorways and dual carriageways when what it actually means is don't turn left into the slip road.
They are good for getting you to your exact destination if you are unsure, but you are far better off knowing roughly where you are going and ignoring it if it tells you something stupid.
For that, I would say the cheapest TomTom is just as good as the most expensive. They all use the same software after all.
All satnavs do not use the same software (partly due copywright) nor do they all use the same satellites for their GPS . It follows that some are more accurate than others,and it has to be said that in my experience, you get what you pay for in this field.