Direct:
- you get a few perks, the main one is the discount on the AP. They also do some special parties during the year and you get 20% merchandising discount. The problem with buying for the perks is that they are not guaranteed at all. They could change or be removed at any time and DVC has a new VP, so she might decide the perks are not really a good idea and cut them all or she could remove those you might be interested in and add others you cannot use.
- it's easier and quick if you want to purchase the resort they're currently selling (Copper Creek and Aulani); some sold out resorts might require a waitlist or cannot be purchased at all
- you get a tote bag if you purchase while at WDW
Resale:
- it's cheaper
It's up to you to decide if the cost difference is worth the extra perks you get direct, common knowledge is that it's not. A possible alternative is to buy the bulk of your points resale and then add 75 direct, which is the minimum amount required for the perks. You should buy resale first, because it's easier to match the direct contract with the UY you bought resale, the other way around would limit you in which contracts you can buy.