Just unlucky most likely - my AV80R works perfectly. The Car navigation is good - works with postcodes too. I prefer it over a Tom Tom unit I have, and it niftily zooms out when you're on a motorway or don't need to turn off for many miles so you get to see town/place names you're passing rather than just looking at a "road line" with arrows the whole time.
No problems with route finding - around the same as the Tom Tom, but both are less "effective" at getting the best route than my built in RTI sat nav in my Volvo (comparing the suggested with local knowledge - the Volvo gets closer to the way you'd likely go in real life for no apparent reason - both the others stick to main routes regardless of setting).
I also like the analogue volume control and the "air hostess" ping noise it plays before annoucements. It also has a nice trip/stats page.
Not used the Garmin, so can't offer an opinion about it - it looks pretty good and from another thread does IFR/Airways.
The AV80R also does music/photos/movies and ebooks - not massively useful per se if you have an iPod/iPhone/etc, but I have popped a few movies/albums on it and it works quite well with the built in speaker.