I still use the activity and route editors within MSTS, but no longer run the sim itself. For about the last year, I've been using Open Rails. Yes, it has its glitches, such as locomotive exhaust that looks like smoke from a forest fire, and digital cab readouts being huge, but these, and others, have had workarounds established. After doing some tweaking, Open Rails runs and looks great on my system. MUCH more stable than MSTS, which used to crash about 25% of the time. Now I can run a route from point to point without having to worry about saving every 15 minutes because of the dreaded crash.
This is nothing against MSTS... it will always be the original sim for me and is what got me in the train simulator realm.