The largest, by far, is Chambord.  Impressive, but somehow unattractive.
An over-blown monument to a megalomaniac.

Absolutely heaving with tourists.
As you can see, tempers were getting frayed in some of the more crowded rooms.    

We enjoyed our visit to Chaumont, though it is a very functional fortified hunting lodge.  Be sure to visit the stables as well.

The famous Chenonceau is the most beautiful.  The grounds include a renovated farm and a full day could be spent here.