The short answer
Glenwood is one of the few hot springs towns where lodging location changes the trip. Glenwood Hot Springs Pool, Iron Mountain Hot Springs, Hotel Colorado, downtown restaurants, the pedestrian bridge, the train station, and the river corridor all sit close together, but not every stay serves the same kind of traveler.
Families usually get the cleanest trip from the Glenwood Hot Springs Lodge because pool access is central to the stay. Couples and adults comparing Iron Mountain should think more carefully about whether they want the big historic pool, smaller riverfront mineral pools, downtown restaurants, or a quieter base west of town.