I have done both and can honestly say that both tours are wonderful. KTTK gives you a comprehensive look at the MK. The Backstage Magic tour adds Epcot and MGM to it. BM includes an up close and personal encounter with the backstage workings at the American Adventure. After a few more things and a look at some of the cast areas in Epcot it is off to MGM and Creative Costuming. Here you get to see where all of the specialty costumes are made. You tour a few more areas and then it is lunch at Mama Melrose. After lunch it is off to the MK. There is some overlap between the MK portion of BM, but with BM you will not ride the rides like you do on KTTK. If money is not the issue, then I say go for BM. Like I said, both are wonderful. In fact I like both tours so much that I have done KTTK several times....and am taking my niece in June, and BM twice. You will learn SO much about WDW on both tours.
Linda