HI Dutch,
I have Nat Geo Topo but I have not used it very much. For over ten years I have depended on My Topo's Terrain Navigator software. It, quite simply, is the best topo software I have seen. It is filled with ability and the maps are first rate and very nicely reproduced. I do think that Nat Geo is a bit easier to use and learn but the trade off is Terrain Nav is much more flexible and capable. It is also more expensive. But you almost always get what you pay for. The need to know exactly where you are or to plan treks accurately makes the added cost worth it.
I assume you will be using the software on the trail. For this TN is great. For navigating cities it is less good because that's not its purpose in life.
I run TN on a Panasonic Toughbook lap top mounted on a RAM articulated mount. It is interfaced to a Garmin GPS which gives real time vehicle tracking. The map source is entirely the USGS topographic series at several different scales. On the trail I use the 7 1/2 minute (scale 1:24,000) maps. On the highway I switch to the larger scale of 1;100,000 or 1:250,000. This is appropriate for the road speed and distance covered.
If the USGS has mapped the area of interest you will see it on your computer. If they have not then..... The USGS maps are not always up to date but Nat Geo suffers the same problems.