One more possibility to further confound the issue: Chaumont, half-way between Blois and Amboise. Chaumont is historically tied to Chenonceau.
Henri II gave Chenonceau to his lover, Diane de Poitiers. After he died, his widow the Queen, Catherine de Medici, insisted - as a Queen of Medici blood could - that Diane give up Chenonceau, in exchange for Catherine’s chateau, Chaumont.
The gardens at Chaumont are wonderful. Not so formal and with a good number of “rooms” or smaller, inward looking gardens. The chateau, which overlooks the Loire, is quite graceful.
Amboise feels (and is) smaller than Blois, though it may also feel more ‘touristy.” And Amboise has the added attraction of Its own chateau on the hilltop overlooking the Loire, as well as the more enchanting (in my opinion) Clos de Luce, as mentioned in another recent post. https://community.ricksteves.com/travel-forum/france/best-ways-to-see-chambord-and-chenonceau
Both Chateau Amboise and Clos de Luce are easily walkable if you stay in Amboise. Chenonceau is a nice bike ride away if you choose to bike rather than go by car or train. Ditto for Chaumont.