Bill, I worked both lines for some time, and have much good to say about both.
First, the D&SNG. Durango and Silverton are great destinations- the stuff of legend- the towns are beautiful and the services are excellent,about 90% and 70%, respectively. There is plenty to do in both towns.
That includes good restaurants (sorry, I always have to recommend the Pickle Barrel in Silverton). Accomodations and just things to do that are non-railroad make other family members very happy. Plus in Durango there are all services needed, including medical. The ride? It is total Colorado. High and incredibly majestic mountains above the solemn beauty of the Animas Canyon, with the river always clsoe at hand. The roster of heritage cars is the very best on ANY railroad .The D&SNG's customer services is among the best in the business. My only complaint is over the years management has "schooled" most of the spirit of the "Old Narrow Gauge" out of the operation. There is a high turnover in employees on the train,and that is never helpful to repeat business. Also, the urban growth of Durango makes the trip up the Animas Valley less interesting than the C&TS east end.
Now,the Cumbres and Toltec. As destinations, neither Chama nor Antonito offer much, with services about 40% and 25%,respectively. Once the train is in,the towns essentially close. Chama offers a couple of good restaurants (I recommend the High Country on the south side of town)and Trackside Emporium and The Hotel in Chama stay open later and are great railfan hangouts run by true characters out of the Old West who are railfan-friendly. For families the pickings are meager. Alamosa would make a better base,plus now you have the option of a steam train up La Veta Pass. Also you need to see the Great Sand Dunes,heaven for kids. The C&TS trip? I happen to like the East Side, as it offers sweeping views of the San Luis Valley and the Sangre de Cristo Range. Eastbound trips are usually very clear, and you can see the entire range,from Mt. Ouray to Truchas Peak. Westbound trips are also good as you can get this part of the trip out of the way early. Once in the Conejos Range, this is an exceedingly beautiful railroad. You follow Los Pinos Canyon for many miles, and can see houses in the bottom that date to the days of the New Mexico Territory. The lonliness and beauty of the ride to Cumbres is one of the last places you truly feel you are seeing The Old West. Unlike the Silverton train the Cumbres Line gets out of the canyon and crosses a mountain range, as does the new SL&RG. I do not know what the present state of customer service is on the C&TS, but I hear it is better than the abysmal state it was in a few years ago,as the new operators adressed this problem first. The crews are long-timers mostly,local guys,and generally the friendliest anywhere. The feeling is much lower key than the D&SNG. There is one other thing about the C&TS. You can wander among the largest collection of narrow gauge cars in North America. It is truly is "railraoding's last great place". It is authentic to the hilt,period.