I've never been to the KTTK tour but I've done Backstage magic several years ago and it was awesome.
We get to go to the utilidoor underground, costume area, parade control room, etc. etc. it was great.
I'm doing this again during our disneymoon because my DF has never been on the tour before and I promised him we'll get to do it before we have kids
Good luck deciding!
Just to let you know that BM tour sounds really expensive but it's actually not bad.
Considering you get a lunch at Whispering Canyon and about 6 hours of tour and transportation $199 isn't too bad.
If you have Disney visa you get 20% off, if you are DVC member or has an AP it's 15% off... not a bad deal at all.
I have a disney visa so ours totaled about $320