We have done Keys to the Kingdom multiple times and obviously love it! We learn something new every time. We have done Behind The Seeds and Backstage Safari.
As far as bang for your buck, BTS is the hands down winner. It is pretty darn educational too! It is a couple hours and basically is an in depth look beyond The Land ride.
KTTK is in MK lasts about 5-6 hours (walking/standing) and details many features and history of MK, Main Street and Walt's vision. You are fed lunch at Columbia Harbour House, you get an exclusive pin and you also get to line jump a couple rides.

You are also taken back stage and into the fabled utlidors. Your guide gives you ample time to ask all those burning questions and rumors you have always wondered about too.
Backstage Safari is obviously in AK and it details the operations of that park and most importantly the care, feeding and challenges of taking care of large animals. We did get to go into some of the barns but we never got to actually interact (touch/pet) any of the animals. We visited the feed house and saw the menu books and prep work for feeding all the critters. This tour was a combo walking and driving with a rest break in the middle of it. We also received a insulated mug with the tour logo on it.
Soooooo, depending on your area of interest, that would really drive your tour choice. If you are just looking for a general tour try KTTK or the Backstage Magic. Your budget may drive your final choice...