Disney has no resales.
The only way to buy BWV or OKW is through resale. There are several resale companies mentioned often. We have never really heard of a bad experience.
There is really no reason at all to buy from Disney. The only possible reason is to get BCV when it opens. There is some benefit to their financing if you would have a problem elswhere. There is no difference at all in your points or membership. The only real difference is that you would have paid less and possibly own at a resort that they no longer have available.
OKW is probably the best choice, at least it was and still is for us. OKW is only available through resale. There is a very actie resale market.