I've used a Garmin for over 3 years and find it great. Sometimes it takes a few minutes to find the signal, but once it is locked on I have never seen it lose it.

I have a US Cellular phone and they provide an Andoid app Your Navigator Deluxe. I have found it to be just as good as the Garmin, but the volume isn't loud enough to be heard over the radio (and I don't have an audio input in my car radio), so I don't use it as much as the Garmin.