Hi Jennifer!
I'm glad you're interested in taking one of the tours at Walt Disney World. I've taken a few of them and I've been blown away each time. The cast members who guide you are very knowledgeable and make it easy to share in their excitement for all of the amazing things that Disney does for its guests.
If I had to only choose one behind the scenes tour to recommend, I think
Disney's Keys to the Kingdom Tour would edge out the others. (It would be a photo finish though because I've loved every tour I've taken!)
When I took this tour with my wife, we got to go "backstage" and see some of the areas that are off-limits to guests. Not only that, but our tour guide also took us on a couple of the classic rides and shared some interesting secrets about them.
Above all else, the thing I enjoyed the most about this tour was how our tour guide shared a number of stories about the development of Walt Disney World and the continual development that has occurred over the years. It really made me gain a greater appreciation for all of the work that Walt Disney and the Disney Imagineers have put into the experiences we, as guests, have enjoyed through many years and stages of our lives.
Sometimes I think it's hard to pinpoint the exact reasons why I love Walt Disney World so much. My best guess is that I, on some level, feel the love and passion that has been poured out by the Disney Imagineers and cast members to make every little detail of the guest experience so amazing. After taking Disney's Keys to the Kingdom Tour, my eyes were opened to just how deep that love and passion runs.
I hope that helps seal the deal for your plans to take a behind the scenes tour. Feel free to stop back by the Disney Parks Moms Panel if you need any other ideas or tips as you plan your next Disney vacation!