I did this ABD in 2008 and loved every minute of it. It was an amazing way to see Peru. I have also traveled in Europe on my own, but this was a destination that, to me, seemed "better safe than sorry," so we wanted to go with a tour.
I would highly recommend the ABD. However, since you are looking at other options, and want max Machu Picchu time, you may want to look at Classic Journeys as well. I just got their new brochure in the mail, and see that their current Peru trip features two days at MP for the family tour and three days for their cultural walking tour. (staying in Aquas Calientas though, not at the Sanctuary.)
Whatever you choose, I second sjlsk8r that it's worthwhile to enjoy as much of Peru as you can, as opposed to just the MP area. It's an awesome country!