Recently purchased the TomTom XXL540. So far I like it but there are a lot of features I need to try / get used to using. Mapping is fairly good - sometimes I prefer a different route, sometimes it gives me good routes that I had not tried (but turned out really good). I like that it uses a Linux OS.
One time the voice instructions didn't follow the displayed route (display was correct) and one time it rebooted itself. No other anomalies.
Display is large enough and clear. Has day/night setting that works well. Updating has not been a problem, just a little slow. Maps appear to be up to date (so far). Some POIs are out of date but the "community update" ability will eventually weed that out.
After doing a lot of research and talking to other GPS users, I don't believe there is a "best" unit or company out there - most seem to be fairly good.
Regards,
GEWB