That really depends on your personal circumstances! If you are fine with staying at the original 14 resorts (and don't mind being locked out of Riviera and future resorts), and want to save as much money as possible, buy resale. You'll save a lot of upfront money that way. You can often save 25%-50% off direct prices (for example, within the last two years: BRV was $176 direct (now $186) and I got it for $93 for 168 points, a 47% savings; CCV is $220 direct without incentives, and I got it for $134 for 100 points, a 39% savings - though admittedly direct incentives would have made it $205 direct, so the savings is 35%; AKL was $176 direct, and I got it for $104 for 120 points, a 41% savings; SSR is $165 direct, and I got it for $95 for 100 points, a 42% savings).
If you are looking at Riviera, there are some great direct incentives right now (likewise, if you are considering Copper Creek or Aulani, there are also great incentives). If the Direct Benefits - access to Gold AP and Platinum & Platinum Plus APs, Moonlight Madness, dining & shopping discounts, etc. - and the ability to book at Riviera and future resorts matter to you, then you will want to purchase Direct.