Hi all,
Chateau Versailles is arguably the grandest Chateau in the whole of France. That, and coupled with its proximity to Paris, also means it's usually packed with tourists, and the queue for admission tickets often snakes for a hundred metres or more especially during the summer. But it does move quite fast.
The chateaus near Tours and Ambroise that we visited and we felt are worth visiting are:
(1) Chateau Chenonceau, the "ladies" Chateau as it is shaped by a few influential women. Part of the chateau spans over a river.
(2) Chateau Chambord: grand and impressive chateau, but not much in terms of interior furnishing.
(3) Gardens of Villandry: wonderfully manicured gardens that are a sight to behold.
(4) Chateau Montressor: little-known and thus not-crowded chateau in one of the prettiest villages in France. Charming.
I'm sure there are others that we missed out, but we were only there for one week.
Typically expect to pay about EUR 7 - 8 per person for admission to each Chateau.
The easiest way to get around is to rent a car and drive on your own; not all the chateaus are easily accessible by train.
Regarding the Champagne region, the main towns are accessible by train; but it's only really interesting if you visit the small producers that produce cheaper yet unique Champagne (large produces spend a lot on marketing); and that again, requires your own set of wheels.