Just finished a trip to the mountain regions of California using a new Garmin 2550. It performed flawlessly, and was useful even where I knew the route just using the Map Mode. Due to California law, I placed it in the so-called "beanbag" dashboard mount, and that was great. Easy to hide when stopped for a meal or overnight.
I selected Garmin because of prior experience with them - they were initial developers of GPS systems for DoD back in the 80s. I trust their accuracy.
BTW, this thread belongs in Mobile Devices and Gadgets, and I will request it be moved.