We vacationed with one set of grandparents and our family of four (2 adults, 2 kids) and stayed in the treehouses, then a few years later vacationed with the other grandparents and stayed at AK.
We really enjoyed the kitchen, eating, living room area at the treehouses, and being all together. Our stay was pre-remodel (back in the days of the Disney Institute it still had the bunk beds in the "trunk" on the lower level). I agree that transportation from our unit was not always optimal. But, it's actually not much worse than the large moderates like CSR (which we also stayed at with extended family). The treehouse them is something our kids still talk about. It was very cool. Sadly, I think in the remodel some of the features (like the trunk in the middle of the main floor) have been removed.
For our stay at AK we splurged on the savanna view and requested (and received) connecting rooms. It was wonderful sitting on the balcony watching animals, but there was not room (or chairs) for six. And, no real area in the rooms to sit and relax together. We did bring a small microwave to heat some breakfast foods, but that is not as nice as having a small kitchen area. The pool at AK is awesome, as are the areas in which animals may be viewed. I think we all agreed that AK was better themed and more enjoyable overall, even without a place to relax together.
For our most recent extended family vacation (9 total - kids grown, plus one grandchild, and great grandparents) we stayed at CSR and decided that our prior vacations of trying to save $$$ by having some meals in the room was not worth the effort. We enjoyed the property even without a central area to relax together. Our together time was in the parks (at various meals and meet-ups) or dining at the resort. Buses can be a challenge at any resort with multiple stops.
So, if I were to chose today between the treehouses or AK, I would go with AK.
Have a great trip, regardless of where you stay!