Chuck,
I run both also

. Aside from Cajon Pass, RailWorks' California content is limited, though the the visual and operational capabilities leave MSTS in the dust. So, my time is split:
-If I need a dose of eye-candy, or if I want the switching to really mimic real life, then it is RailWorks. Still getting the gist of Scenario building, so much of the action is free roam with a "plan". Loading and unloading passengers and freight is powerful enhancement. Mostly running Rich Garber's Colton & Northern, mixed with Castle Rock and Cajon Pass.
-For full-blown activities, lasting up to ten (10) hours--generated by Steve Davis's Activity Generator--it is MSTS, using Cajon Pass (both versions), Feather River, Cascade Crossing, BNSF Scenic, or Tehachapi II.
My gut tells me that RailWorks is the future, and its stability is also a big plus.
Dave
Benicia, CA