I've a Garmin 62S (as well as an older 60CSX). I went for the one without preloaded mapping as it takes up some of the available memory, permanently I believe. I just load whatever maps I want for anywhere in the world as and when. (I get my routable maps from
here which are based on
OpenStreetMap - which you could contribute to using tracklogs and waypoints from your new unit!)
One thing I like about the 62 series - made me upgrade from the 60CSX - is being able to calibrate (georeference) satellite/aerial images or scanned maps and then load them into your unit getting your position overlaid on the imported image. Garmin will sell you aerial images but there's stuff around you should be able to get gratis. Some national mapping agencies provide digital versions of their maps free so you can grab those too.
The unit seems to keep the signal very well in thick forest and in deep canyons, and works fine in the car without an external aerial. It's chock full of features such as altimeter, which seems pretty accurate (depending on satellite geometry), compass and other stuff I haven't found or used yet. But it is an expensive unit if all you want is a simple backup for your regular nav.
If you go for one make sure you upgrade the firmware as the early firmware versions of the 62 series were a bit adrift on the speed and distance shown on the dashboard display, along with one or two other "undocumented" features.