The United States Geological Survey (USGS) has created numerous maps for all satellites of the solar system. A very popular one is the gray-scale shaded relief "texture" map:
The USGS texture map of course comes in different resolutions. The demo version comes with the lower resolution texture map of about 5 km (3 miles) per pixel suited for the casual observer, while the registered one goes down to 0.5km/pixel, which matches the resolution of the Clementine imagery. Images courtesy USGS Astrogeology Research Program.
To put Lunar Calculator into USGS mode, select the View menu and choose USGS:
You can pretty much find this basic texture map on any software that renders the Moon in 3-D. This map has the distinct advantage over Clemetine imagery in that it attempts to show the topographic relief of all features visible at low sun angles, with a morning illumination (which is in the evening hours for earthbound observers). As noted in the Clementine section, when the sun angle is high (more than 45 degrees from the terminator), the craters begin to disappear and the ray systems become prominent. When this happens, the "texture" map is a woefully inadequate representation of reality. But with a low sun angle near the terminator, the same can be said of the Clementine imagery. Use the one more appropriate to your situation.
So obviously the thing to do is use the best of both. The blended choice does this, although at a cost of more time to generate the image. In my opinion, the result is clearly superior. Since the processing time increases in a blend situation, you may want to speed things up at higher power by using only one of them, when the other is inadequate. For example, if you are working along the terminator at high power, you may as well not blend in Clementine since it is faded to near zero anyway. Likewise, under high illumination you should use only Clementine imagery since the USGS values are faded to near zero.
Another problem with the USGS texture map is that far from the terminator, the craters no longer have shadows. So Lunar Calculator reduces the amount of shadow and bright rims. What's worse, after full Moon the lighting comes from the other side - the shadows and highlights are now incorrect. You can overcome this by using Lunar Calculator's "Dynamic shadow USGS".
Both the USGS texture map and Clementine imagery are produced with "constant illumination", which means that neither replicates well the difference in brightness going from the terminator to a high sun angle. You can adjust the amount and character of the terminator shading to suit your personal taste. You can adjust the values in the "Contrast, Brightness, Terminator Shading" section.
When you superimpose craters on the USGS map, you will sometimes see features that don't quite line up. On the rare occasion, this is an error in the feature database, but most of the time the problem is with the texture map, which was created well before the highly accurate mapping from Clementine. If you switch from USGS to Clementine view, you will see that the Clementine image lines up much closer. As mentioned in the database section, it can be difficult to have an accurate diameter for a complex crater, so the most common form of "error" you will see is that the circular crater overlay appears too big.
Yes they are. The lower resolution maps have darker mare regions. I'm not sure why, but that's what is available.