Welcome to AFF.
Sorry, can't really help with the "best" place to sell, but once place that has been mentioned here before is
Redseason.com.au - Trendwest (Worldmark) and Accor (APVC) memberships at discount prices. You can sell to them directly
"Selling Your Membership
Sometimes, for one reason or another, it's just makes sense to sell your Worldmark South Pacific or Accor Premier Vacation Club Membership. At Redseason.com.au, we make the process quick and easy. We buy your membership outright, and the price we quote is the price you get. There are no gimmicks. No advertising costs. No waiting around to find a buyer. And you'll receive your money soon after we receive the transfer documents. Please note that all buying prices are determined by an individual evaluation of your particular membership - we cannot give a price based on a general description such as "6000 credit package".
"
There are likely to be many other ways to sell your membership. I'm sure I've seen them being sold on EBay for example. But sometimes, you just have to accept a quick and easy way to get some money back vs a long and drawn out selling process.
Good luck with the sale. As I mentioned above, I know little about timeshare selling, so best you look around at various sale options.