Buy at the resort you'd most like to stay at, especially if it's VWL, BCV or BWV as these places can be very difficult to get during certain times of the year. SSR is cheaper and gives you 10 more years, but is that worth all that much if you run into trouble staying where you want to be?
Advantage to buying resale is that you'll save a few dollars. Probably on the order of $10 a point or so. How much depends on what kind of deal you get and what kind of incentives (if any) DVC is offering. If you want a sold out resort it may be quicker to go resale.
Advantages to buying from Disney are that the process will be easier, closing will be quicker, and Dinsey offers financing. Disney will give you a tote bag.
Otherwise, membership via either route is the same.