I believe Topo USA uses 1:100,000 topo maps as its basemap, NG Topo uses 1:24,000 maps for it. They are much better for that in my opinion, Delorme does have a topo mapping product based on the 1:24,000 scale maps, but I don't have any experience with it. Besides, I don't think that they offer the downloads like NG Topo does on its mapxchange.
And neither of them match up to Google Earth where the imagery resolution is good. Especially for free.