Buying from Disney:
1. Your option is SSR (not a lot of SSR resales, but if you really want SSR, you can find them, if you are patient on the resale market - and in a year or two, you'll find more of them).
2. Financing is easy
3. SSR has the 50 year deal going (for us - in our late 30s, we aren't interested in being in Disney in our 80s, so we don't care).
4. Once they get your deposit, you'll immediately be able to make reservations - important if you are planning a near term trip.
Buying resale:
1. Usually cheaper - although you will pay closing costs
2. Availability of the other resorts to choose from
3. Resales can take a while to close (two months after the offer, or more, sometimes) and you can't make reservations until you are in the Disney system. Resales are not good for people with plans to use points in the short term.
4. You have to pay more attention. The point distribution (how many points are current,how many borrowed, how many banked, how many will come next use year) can add or subtract a lot of value to the contract in question.