You can get the exact number of points that you want (although you must buy a minimum of 160)
Faster than resale (you will be in the system and have your points and be able to make reservations much faster than resale)
No worries about the purchase if Disney executes ROFR, since that only applies to resale purchases
More expensive cost per point than the resale market
You can finance through DVC, and Disney doesnt report the loan to credit reporting agencies
You can pay with a Rewards credit card and get points/cash back
The full set of points you buy will be available immediately, versus a resale contract which may be stripped of points.
If you dont want the resorts they are currently selling (AKV/SSR), you may have to do some firm talking to a guide to convince them you really want an older resort.
Initial Purchase via Resale
You may not get the exact number of points you want
You can purchase less than 160 points for your initial buy-in to DVC (Disney wont let you buy less than 160 points).
It will take much longer to get into the DVC system and have your points (resales typically take 6-8 weeks)
Disney may exercise ROFR and you may loose the resale and have to start all over (When buying resale, one of the potential pitfalls to try to avoid is making an offer that will cause Disney to exercise its Right of First Refusal)
Resale is typically less expensive then buying from DVC
You cant finance through DVC, although most resale brokers will recommend a finance company
A resale contract may be stripped of points where the user has used many of the current years points, and may have borrowed some or all of next years points. Be aware of stripped contracts on the resale market.
Easier to pickup large point packages at any of the older DVC resorts.