I have done Keys To The Kingdom, Backstage Magic, Behind the Scenes at Animal Kingdom, The Sunrise Safari Tour, and Diving with the Dolphins.
All of them are great in their own way.
Diving with Dolphins is in Epcot and it was a lot of fun, but not as much Dolphin interaction as I had hoped. It's a lot about learning how they care for, treat, and train the dolphins. Then you get in a wetsuit and go on top of the Living Seas Tank. You're in about 3 feet of water and they bring a dolphin out for you to pet and take a picture with.. and that's it. It was really cool being in the actual tank. Especially since the fish are not afraid of you and will come up and bump your leg to see if you're edible.
The Backstage Animal Kingdom tour is very informative. You see how they keep the animals, learn about feeding and care, and you get to go into the actual animal hospital. You also get on KS without waiting in the big line.
The Sunrise Safari Tour was AWESOME, but you can only get it if you are staying at AKL. Basically, you take the KSJ ride before the park opens, when the animals are just let out of their pens. They're frisky and very much awake. You don't have the corny story going on, so the guide can tell you a lot about the ride itself. Then you have breakfast at one of the restaurants and you're in the park when it opens.
Backstage Magic goes to all 4 parks and behind the scenes of several attractions. It's a long day.. from about 7am to 4pm. Lunch is at the Ft. Wilderness Lodge. I enjoyed it, but our tour guide seemed to be phoning it in. You don't get on any attractions, but you do get premium viewing for Mickey's Jammin' Jungle Parade as that's the end of the tour. You see a lot of the support facilities.. costume shop, ride repair, gardening and all that's very interesting.
Keys To The Kingdom was the best. Lot's of backstage stuff, we rode a few things (Jungle Cruise and HM and, I think, Pirates) Lunch at Liberty Tree Tavern. The Utilidors are amazing (you see them on the Backstage Magic Tour, also). I really loved seeing the the backside of MK and learning a lot of the little known history of the park.
I think I would rank them in favorite order as:
KTTK, BM, Sunrise, Backstage AK, and Dolphins.