I would recommend the Garmin sets with the usb computer link and the free Garmin Mapsource software. Planniong an interesting route is not at all easy on the small screen of a satnav, but the PC link allows you to plan a route on the big screen, zap it down to the satnav and then follow on the road. this is a far moire useful option if you are "out for the day" as opposed to simply going to a destination - allows you to chose your route rather than just the fastest or shortest.
dont know about the TomTom but my old Garmin allows you to set typical speeds for different types of roads as well as to set avoids for different types of roads so when it works out the quickest it does so on realistic times.
