We plan to follow Rick's advice and limit our visit to three chateaux in the Loire valley. Based on our itinerary, I have narrowed it down to Chambord, Chenonceau, Saumur, Chinon, and Chaumont. I am leaning towards visiting the first three I have listed. Your comments and experiences are welcome.
John, we've been to all of those chateaux and many, many more. Chenonceau is nice, but a crowded tour bus mill. Given the choice I would take Chaumont over Chenonceau. The hunting dogs at Chaumont are fun. Many tourists at Chambord too, but it's spread out and in a nice setting. And it's just too awesome a structure to pass up. Take advantage of the free half hour tour in English. Saumur also very good. Beautiful setting. If you have time, I would lobby for a trip to Breze which is only a few miles from Saumur. Off the beaten track, not crowded and VERY interesting. Here's a link to their website: http://www.chateaudebreze.com/gb_fram.html
John - Chenonceau is fabulous first thing in the am. I liked Chambord OK - the trophy room and the Da Vinci staircase are magnificent. My family really loved Cheverny - you get to see a letter from George Washington thanking the family for their help with the American Revolution but the best part is to be there when they feed the hunting dogs. We were there in 2004 and my 11 year old son is still talking about it! Have fun!
My absolute favorite is Chenonceau. Not only is it a storybook fantasy castle, but the gardens, location over the river, and beautiful huge dry or live flower arrangements that are placed in many of the rooms are spectacular (and have been there each of the three times I have visited there). My second recommendation would be Chambord - everything is done on such a large scale. I have visited Chaumont, and think it would be repetitive if you have seen Chenonceau - and there were somewhat corny displays on the interior. Chaumont is adjoined to a small neighboring town, but I didn't think it was anything special. I really liked Villandry as my third, because of its ornamental kitchen gardens - something unique to this property I believe.
I would highly recommend also staying in a chateau in the Loire Valley - there are many privately owned that are spectacularly kept - last time we even stayed in one owned by a count and countess who also lived in the chateau!
My absolute favorite is, like Tamara above, Chenonceau. It is not a "tour bus mill." It is the best, in my opinion. I would put it at #1 of them all. In addition to what Tamara wrote, just the walk up to it is magical, the long driveway covered by the beautiful trees. To the right of this long drive, is a "farm" and beyond that, towards the chateau, is what looks like a storybook little village where the workers lived. We spent 7 hrs there last time, it was so enjoyable. We could easily imagine what it was like 400 yrs ago. They also have a wonderful cafe and a classy wax museum of all the "players" of the day and a background story on them which helps make it all come alive, which you won't find anywhere else. If you walk through the chateau and out the other side, there is a forest which we enjoyed walking through a bit, and along the river, in front, to the right, is a path along the river for walking or biking. If someone only had time for 1 chateau, I would recommend this one.