Garmin.... We own a Nuvi 200 and and 205W.
Before we bought I talked to a sales rep at both Radio Shack and our
Best Buy. I asked them for their impressions of the top sellers. They both replied that the top two selling brand were the TomTom and Garmins, but that they thought the interface on the Garmin was a bit better and easier to use. Overall they've had more people return the TomTom units versus the Garmins.
The sound on it has gotten rather strange. Sometimes I can't make out the name of the street they're saying.
Unless you find a good sale on one, I'd save the extra money you'll spend on a "text to speech" unit. Neither of ours has it and we don't miss it. It calls out the turn direction and counts down the distance as well as displays the street name of the turn in large letters so I can read it at a glance.
Navigation is also just as easy with the wide screen as the narrow, but the wide screen allows for a QWERTY keyboard that's easier to use.
While it's true that
most GPS units allow updates to maps, there still are ones that don't.
Lastly, make sure of the coverage of the map. Some only offer US only navigation. If you live near, or plan to visit Canada, your GPS may stop at the border.