Emphasize steam engines and passenger trains over freight or structures. That is what the general public will understand. Show the best featues of the line isteslf that make it a joy for the public to ride, foliage and topography.
-#1 Double headers are great, but flat land is boring.
-#2 is better, shows some Colorado/NM topography and foliage (read pretty) and you still have your doubleheader.
-#3 Nice photo capturing the hills and the old west feeling, but too much emphasis on the freight train.
-#4 would be nice for railfans, but would not be particularly informative to the general public. "Whats that big wood thing behind the choo choo?"
-#5 is Dramatic but doesn't show hills and little foliage. Still not bad.
-#6 - Dramatic, hills, trees, steam - good choice.
-#7 - no smoke, no trees and a tank car which would be confusing. Good for railfans but not public.
All are good photos, bot to convey the railroad to the masses my choices are #2 and #6. #3 and #5 as runners up.