I think the downfall of all GPS units, no matter who makes it is that the mapping from what I understand comes from a 3rd party. On top of that when talking to a tech at Garmin, he somewhat indicated that basically all of them use the same company for their mapping/routing programs. Personally I think it would be a daunting job putting every road, street, highway in the entire US, not to mention Canada, Mexico, and all of the other countries into a computer. Then program a route from point A to point B, and have it come out perfect every time. Can a GPS fail to be correct sometimes, dang right they can & do. Do you want to stake your life that it will preform flawlessly every time? If you do, I've got some bridges & beach front property for sale.
I choose Garmin from past experience, I have been using their units for about 20 years, and have bought about 8 units in that time for different purposes. Garmin units haven't let me down. Sure there have been a few times when I've been led astray, but it hasn't been gross & I survived even though it was aggravating. Garmin has free software updates for the unit, and lifetime map & traffic updates. Granted the map & traffic updates are probably available with other brands. On top of that if you have an issue, or a question Garmin's tech support folks are great, and will take the time to get you through your issue...and it's FREE and good for the life of your unit.
Bottom line, if you want a GPS, do your research, read the reviews, and make the best decision you can based on what you've learned. Personally, I doubt that I'll own another brand other than Garmin!