Earlier this year I bought a Garmin Nuvi
A friend bought a TomTom.
They both have slightly different features but out of the two the Garmin wins just slightly because it was a bit more precise finding places whereas the tomtom had other features that could be seen as plusses.
You can change the garmin from Car to pedestrian or bike mode.
And the way it makes choices about routes can be changed, "quickest route" "Most direct route" "no toll roads or charges"
etc
They are a great bit of kit and if you have no idea where you are going then they are a lifesaver, if your just getting it to pick the kids up from school everyday then don't bother (unless thats a 100 mile journey and you want to take some detours)
I like the fact it recalculates your route if you decide to take a detour because the traffic ahead looks busy or you just get wanderlust