Re: D&S or CATS???

Both are well worth the visit, but given your contraints, I 'd opt for the C&TS:
1. Chama is closer to ABQ than is Durango....more time for looking around.
2.The C&TS is like taking a trip back in a time machine. As others have stated, it's very informal, and as long as you're doing things in a safe manner, no one will distrub your wanderings.
3. The Mudhen. This little beast has a rifle sharp exhaust, and is a delight to hear as she labors up the 4% with one of the other larger mikados.
4. Four per cent grades
The scenery on both is spectaclar but in this regard I might give a slight edge to the D&S. The scenery on the C&TS is more varied. You won't be disappointed regardless of which choice you make.