I've done the Backstage Magic (Epcot and DHS as well as MK) and the Keys to the Kingdom tours and for me, KTTK was a much more thorough tour. It was really interesting and at a nice leisurely pace too (BM felt a little rushed at times).
If you're interested in learning more about MK and seeing a little (although it's only a little, we got to see all of the parade floats parked up, and we got to see the back of Splash Mountain, both of which were super cool!) backstage stuff, I'd definitely recommend KTTK, no questions. It was a great tour.
There's quite a few discounts off so ask, but I think it's worth it anyway.
our backstage magic wasn't rushed at all - very liesurely, and we saw so much....and of course, all of it was backstage...also, we did all 4 parks....
we started at epcot, then DHS, then lunch, then MK, then AK....
i loved every minute of it..
actually, i've done many of the behind the scenes tours....last june, when i was on my first solo trip, i did 8 tours.....all very interesting...
and i've done a few with the entire family as well...
i'm coming back to edit - i just looked at the list here:
http://www.wdwinfo.com/wdwinfo/tours.htm
of the tours listed there i've done the following:
-- Backstage Magic
-- Backstage Safari
-- Behind the Seeds (with the family)
-- Dolphins in Depth
-- Epcot Aqua Seas Tour
-- Nature inspired Design
-- Segway Around the world (twice with the family)
-- Sunrise Safari (with the family)
-- The undiscovered future world
-- Wilderness Back Trail Adventure
-- VIP tour (with my mom and sister - they joined me at the end of my solo trip)
as to whether i'd do any of them again, yes...i would be happy to do all of them again except for the VIP tour....the regular behind the scenes tours are all different and all well done....