Welcome aboard Jim - I'm BigVern from UKTS (retired) and Northern Warrior from T-S.com. There's quite a few of us with interest in more than one sim. Development wise I haven't touched MSTS for about 4 years now though I still open it for a quick route blast. I've done a couple of routes for RS but found it hard going and time consuming, never got very far with Railworks and of course the latest bug has rendered it useless for route building until/if RS.com sort it out. So I've very much embraced Trainz though I tend to work in TRS2006 as I find that the best and most stable version for what I want to do. The DLS can be a bit 'ornery at times but for the most part it does what it says on the tin - a vast collection of scenery etc. items in there. In particular check out the trees by JVC and DMDrake (also the latter's range of US building sets including prefabricated city blocks, a real time saver).
 
Transdem and the link to WMS (so far as US routes are concerned anyway) is an extremely powerful tool. Unfortunately the maps can look a bit blurry on the ground itself but if you open the minimap, things tend to look sharper and you should be able to see the key features. In addition, I normally find the appropriate GIS site for the State(s) concerned and download the relevant 1:24000 raster map tiffs so I can have those open in PSP7 while I work in Trainz.
 
It's certainly far quicker getting up and running than in RS/RW (even before the route nuking bug introduced in the last Steam update). I recently started a protolanced project based on the old NYC from Tupper Lake up to Malone Jn. Within about 45 mins I had the DEM prepped, the course of the route traced, 6 - 7 mins for Transdem to find the WMS overlay maps, export from Transdem, import to TRS and I'm laying track. Contrast that with 2 days in Google Earth just putting in the basis marker pins for Railworks, not even started on the lakes and other features which are easy to see on the maps over the tiles in TRS.