I've got the National Geographic Topo program. I also have DeLorme's Topo USA (v.4.0) program.

The NG offering has real honest-to-goodness 1:24K scanned USGS topo maps. The DeLorme maps are, if I remember correctly, based on 1:100K USGS maps.

With NG you are getting all the detail that is on the paper maps, but the user interface leaves a little bit to be desired. With DeLorme you are getting their own seamless interpretation of the USGS maps, minus a lot of the detail. Also, DeLorme's user interface, draw tools, and routing is a lot nicer.

You can buy the DeLorme program in national ($99) or regional ($49) editions now. I believe they are up to version 6.0. The NG program is offered in the state versions for $99.

If I had to buy only one, I'd buy the National Geographic software. You can print maps all day long and you're getting good detail.

This place has the software for cheaper ($79):
http://www.gpsnow.com/wftstates.htm