We took almost every backstage tour last Oct on our Honeymoon. We couldn't ride a lot of the 'thrill' rides due to a recent auto accident, so we substituted these tours. If you are at all interested in the story behind the magic, then any of these tours are excellent. All the tours are a lot of walking, but we found that if we kept up at the front of the pack, we could quickly find a rail to lean on and rest while the group caught up.
We really enjoyed the AK backstage tour. In addition to seeing the animal pens and meeting with some of the keepers you get a couple blessed hours of air conditioned classroom time with special guests. The only thing I would have liked to have seen is a little more of the 'physical plant' (the water ways, shipping and handling, float storage, etc). All in all our favorite backstage tour of the trip.
At EPCOT we took both the WS and FW tours. Although I knew about 60% of the information from the FW tour, our guide was excellent (he helped write the tour) and I did learn quite a bit.
Disneyland offers a Walk in Walt's Footsteps tour where you learn a lot about Walt's motivation for various aspects of Disneyland. A lot of the FW tour was like this and that was the stuff I already knew. So I would have liked to seen a tour that focused more on how all of these wonderous things work. But your milage may vary.
The FW tour is a lot of information spread over a nice walk through the park. It was our least favorite tour of the bunch, but still we highly recommend it. On this tour you really get into the details of each land. Stuff you'd never know unless you took the tour or had a 'native' guide from the pavillion. Our tour guide was excellent, but our largest complaint was she was always waiting for the group to catch up and that made the tour long. We budged an extra hour and even that wasn't enough time and we had to leave to make HDDR that night. I recommend you take this tour *before* you visit WS for the first time on your own. Then when you return, you'll have a much richer visit.
The MK Keys to the Kingdom tour was also very good. I like how it focused on preparing us to be cast members by teaching us the four keys and how they are used throughout the kingdom.
Each of these tours depends largely on the knowledge of the tour guide and how far 'off-script' they are willing to go. I found that if I asked the right questions, they would really open up their storybook and provide some personal observations that added great value to any 'facts' they had imparted.
As with everything, YMMV. But I recommend all four of those tours to anyone who has been to WDW at least once.
