Mesh = Terrain elevation and it's resolution in terms of height and contours this has nothing to do with the look, this is determined by FTX Global's texture files.
Landclass = How and where textures and autogen are geographically placed within the simulation.
FTX Regions = Complete regional enhancements that include all of the above. In addition they also include enhanced airports and autogen specific to the region.
Rocky_53's post in Best Global Texture package? was marked as the answer