Caution: only tested with
MSFS 2002 and 2004

Quality mesh - Some Practical Considerations

The spacing of elevation readings in the source data determining the accuracy/realism of the mesh in the sim. Period. Closer source data spacing means more realism.

LOD, specified by the developer, determines final spacing of data points rendered by the sim, but has virtually no positive effect on realism (compare sample screenshot Images 4 and 5, constructed from the same data using different LOD values). Because the sim uses LOD to determine which of two sets of mesh should be displayed, it is important for the developer to try to specify a final resolution that is close to that of the original. Otherwise, where there are conflicts, you may not see the mesh you expect!

Sources of confusion:
Source Data: spacing may be specified in different units; arcseconds or meters, depending on source.

Developer: LOD specified may not match the source data, implying higher quality than the data actually provides. This may be due to a misunderstanding of the data, or it may be deliberate.

End Users: confused by the issues above, sometime tend to perpetuate the confusion by describing mesh they are using incorrectly.

Learn about your mesh data:

Sample numbers the developer should provide with the mesh
actual sourceapprox source final resspec usedusefulness; what it tells you
  100m    minimum; measure of accuracy
  100m=>76.4m fair; how close are they
  100m=>76.4m(lod 9)better; interaction with other mesh
(3 arcsec) 100m=>76.4m(lod 9)best; if source other than meters

Install your mesh in separate folders so you can test it.

And take screenshots of those tests.

Screenshots reveal all

As a guide to what you can expect from your mesh, I have constructed a series of screenshots showing an approach from the SE to the top of Mt Washington, New Hampshire, crossing over Tuckerman's Ravine. These include examples using all the popular source data resolutions readily available for the USA, as well as the default mesh. (10m, 30m, 100m-9, 100m-10, 1000m, and default)

I recommend downloading these images and comparing them using your favorite image-viewing software. The differences are significant, and may help guide your mesh decisions. There are 6 images at 1200x900 screen resolution = 1.25MB:

download sample screenshots in zip file
view sample screenshots online

With this unique visual information to guide you, you can then properly consider the many tradeoffs you can make when selecting mesh: availability, cost, file size, performance, convenience, ... It is still a personal decision, but you will know what kind of quality you can expect, and how it compares with the alternatives.