I have used the Garmin Dezel 570 for 5 years or so. I really like it and the height setting has never let me down. I tried it around town when I first got it with low bridges and it told me about each one. If I needed another one I would get the 7" model.
RandMcNally 730 worked great for hauling cars, esp around Chicago (the land of low bridges). I did get detoured around a low bridge one time and had to deal with about a mile of low tree limbs.