We bought at BLT because we love the MK and it is our favorite park. We also travel during Magic season, so for us, the point difference for stays in SV rooms is not that much different than the other resorts we would choose (VWL, BWV, or BCV). Owning there to use the 11 month booking window was important for SV rooms.
I think that everyone should buy at the resort that they believe they will enjoy, if nothing can be traded out at 7 months the way they want.
If you are really unsure, have you thought about getting points at both and then doing either split stays each trip or using banking and borrowing to alternate between the resorts each year.
It would give you an opportunity to have the 11 month window at both (with whatever points you buy at each) which may also allow for some customization of trips.
So, if you own 100 points at BLT and 100 at AKV, then you could bank BLT one year and borrow AKV to get 200 points to use at that resort at the 11 month mark.
Depending on when you travel, you may find this useful. For example, one year you want to visit in December and stay at BLT, but the next you are going in the summer and AKV will be just fine.
Good luck!