We have done Keys to the Kingdom, UnDISCOVERed Future World, WS: DestiNations Discovered, Behind the Seeds, Backstage Safari (not around anymore but was kind of a mix of a bunch of the AK tours) and also the Wanyama Safari (twice) and the Starlight Safari both at AKL. We have really enjoyed all the tours we have done so far and I really don't think you can go wrong with them.
While we probably enjoyed our tour guide the most, KttK was probably the least informative and the one that showed the least backstage, but it tends to get the most love on the boards and is most often peoples go-to for a first tour. I'd highly recommend the 2 in EPCOT we did. They are very different tours from each other where one is more backstage oriented and the other is more cultural with some backstage splashed in. Like I said, you really can't go wrong with any of these types of experiences.