Buy the one with the biggest screen and one that allows you to 'speak' the directions to it instead of having to stop and hunt and peck tiny screen keys to enter it. I found both of these options on the TomTom.
As far as bridges go. The GPS is a joke and should never be used for the 'safety' of the height of bridges. Every bridge height recorded on a map or a gps in the Chicago land area are all wrong. In fact in any state that is situated in an area where it snows and gets cold, be real careful.
These roads are resurfaced and resurfaced and resurfaced. Adding multiple layers of road and shortening the distance to the top of the bridges. And they NEVER go back and remeasure and fix the signs or the height that is painted on the bridge. Heck on many bridges, the height that is painted on top of it was put there as far back as 100 years! :W