I have a Garmin and love it. My first nav system. I had originally intended on getting a Pioneer AVIC-D2 (in-dash) but changed my mind at the last minute and figured I'd save some money, while also enjoying the option of putting it in whatever car I was going to drive.
The only time it's steered me wrong is around the DC beltway -- in particular, the Alexandria area, since they have been working on and changing the freaking roads once every few months.
Other than that, it's been great. I've found so many things close to home I didn't even know were there. On my 4 hour trips to visit my family, I've used it to find alternate routes to get me out of backed up traffic on I-95. It's great. Definitely worth the investment.