To me the best to start off with if you and your wife have never done any is Keys to the Kingdom at MK. Me and DH loved it and would do it again! It's about 5 hours and lunch is included. It's very informative and interesting. You also get to go onto a few rides during the tour like HM or Jungle Cruise etc. You get a souvenir key pin at the end when you have lunch also.
We also have done the Backstage Safari tour (roughly 4 hours and includes snacks and a souvenir travel mug) at AK and have done the Sunrise Safari tour that starts at AKL but that one has ended.
We have loved all the tours we have done so far. We will eventually do Undiscovered Futureworld and Wild Africa Trek.
But really our opinion the best first tour is Keys to the Kingdom at MK. That is what we always reccomend to anyone who have never done a tour before. Awesome tour for adults.