Garmin's Topo is about the equivelent of a 1:50,000 scale topo map.... not as much detail as a 7.5-min topo as I'd really like, but good enough for most uses. Not strong on road names.
I like DeLorme's software better, Nat. Geo has some good software; if you're using a laptop to run the software, you can use most any GPS with it. However, if you're wanting to load the maps into a Garmin GPS, then you about have to use Garmin's own software.
-L