I think that it is important to really think about where you would like to stay and consider buying there.
We travel in the summer and so far, have been able to trade out at 7 months to both BCV and BWV (from BLT). However, at 6 1/2 months, those rooms were gone so if you are planning in advance, you should have luck getting to try other place.
If you are really unsure what resort you would be happy with if all others were not available, then just don't choose one you would be disappointed in if that is all there is.
We bought BLT because we knew, regardless of what happens, we would be okay if nothing was available to trade. Even when I called two weeks ago to try and get a BW view 2 bedroom for my August trip, I wasn't worried because had it not been available, I was booked at BLT and perfectly okay with that.
Good luck!