I am a
long time National Geographic Topo User but I just switched over to DeLorme Topo USA and Street Atlas USA, here is why.
The main reason I liked Topo was the USGS maps, that was great. The main issue I have with it is that it really looks like National Geographic is moving more toward an Internet based approach and that is just not going to work with expedition type wheeling in mind.
I got a good deal on the DeLorme software and GPS dongle so decided to give it a whirl. The main issue with the DeLorme software is it does not use the USGS maps, it uses their own maps. This is easily fixed by using their Netlink tab to download maps for a fee. I highly recommend getting an annual subscription which gives you unlimited downloads of maps and aerial imagery.
Here are the features that I really, really like about using DeLorme software:
USGS Maps: These are the same maps as Topo has although not as polished looking and only at the 1:24000 level (only level that really matters to me).
Aerial Imagery: There are a few different flavors of aerial imagery available, this is really handy for tracing out trails and such.
NOAA Nautical Charts: One day I'll have a boat!
Draw Routable Roads: This is the real cincher for me. I can draw roads on the map that are then routable in either DeLorme Topo or Street Atlas. This was I can pre-stage an entire event with routes and have my computer lead me through the entire weekend.
Compatibility: DeLorme makes it a little easier to share than Topo does.
I like that DeLorme Topo and DeLorme Street Atlas can share information well. I can set up roads in Topo using imagery and USGI maps then bring them into Street Atlas. It's easier to build a GPS route in Street Atlas so I load the custom road layers into SA, build and safe the route, then bring it over to Topo for use. I had my machine running with Topo when I was in JV last November and it got the job done very well, it would route me through trails and the big 14.1" display was nice.
The only issue I have with DeLorme software is the lack of Macintosh support, it is PC only. Topo does have a Macintosh side but it's not always on par with the PC side feature wise. I've worked around that issue by getting a PC laptop for my navigation machine.
Here it is in use!
(The red lips looking thing are wilderness area overlays I drew on the maps.)