We have stayed in an MK view three times -- twice on the 11th floor, once on the 8th. Higher is better, although 8 is good also.
I would definitely say 18/20 is a little better than 24/26/28 area. We have stayed in 8124, 8120, and 7824. The reason I say 18/20 is better is when you are viewing the fireworks. From BLT, the fireworks actually explode above Space Mountain. The curve of the building makes viewing better from the more northern rooms.
There is nothing better than tuning into channel 20 and listening to Jiminy Cricket while the foreworks explode outside your window. Two minutes after its over, your in bed! No crowds! Plus, its a lot harder to have a beer during Wishes if you are on Main Street!!!
I know I am in the minority on these boards, but I wouldn't stay at BLT without an MK view. Our "kids" are 24 & 17, so we don't need to be next to MK, but the view is special, especially as the sun sets.
mac_tlc