My wife and I moved to the area a few years ago but still haven't gone on one of these. It looks like there are a ton of them, so I'm wondering if you folks know of any good ones?
Most/all of them are nice. Really close is the Colorado Railroad Museum, which had short (15 minute) rides behind a steam train. Georgetown Loop is a bit longer and very nice. Royal Gorge had nice dinner trains
If you are looking for longer rides, Amtrak to Glenwood, Durango/Silverton and Cumbres/Toltec are all stunning.
I just did the Leadville one. It was pretty cool and nice views but to be completely honest, it was about an hour too long (imo). Also, I have a feeling the other mountain trains might be similar but the seating was uncomfortable. Just food for thought.