My work van has a Garmin Nuvi, and I have a TomTom One in my Jeep. The Garmin Nuvi has more features and is fancier, but the TomTom One is simpler to use and has a better user interface (in my opinion).

So, I actually prefer my TomTom. I even do GeoCaching with it where I take it out of the Jeep and use it to hunt stuff in the woods.

Also, the Garmin seems to talk a lot more than the TomTom. It says street names, whereas the TomTom just says "Turn right".