We are in the process of buying a resale at Boardwalk. Although we haven't closed yet, we are very happy with the decision to date to go this way.
You pay closing costs when you go resale, you don't with Disney.
You may have to arrange your own financing (if you need it). Disney will arrange financing for you.
You may or may not save money (closing costs, Disney incentives).
You can buy sold out resorts, such as OKW. The only WDW property currently being sold is BCV (which you probably can't get as a resale, but if you are interested, give it a couple months - someone will decide they made a purchase they can't afford).
Your resale broker may have more time on his/her hands than your Disney Sales Guide....Disney is very busy right now.
Your Disney purchase may close faster (at least, I've gathered that they close very quickly), and your member number gets in the system faster.
You may be able to find a resale with banked points into this year - this is really nice if you are planning an immediate vacation.
There is a very vocal OKW contigent here. But OKW seems to be the easiest resort to get into at the 7 month window (and that depends on when you like to travel) - so the biggest advantage to OKW is the lower maintenance costs (since, if you can get in at seven months, you get to take advantage of the larger rooms, just like OKW folks can take advantage of the Boardwalk's walk to Epcot or pool if they get in at the 7 month window. We originally tried for an OKW resale, but the seller pulled out. When we switched to Boardwalk, it was easy for us to say "the kids will like the pool better" and mean it. OKW resales go for less money than BWV or VWL (which may mean people value them less, or may mean that they are a bargain). At the same time, low point (and therefore low cost) OKW contracts tend to sell fast, because they are the cheapest way to get in, so you may have to wait for one to show up on the market.