The Four Seasons Resort Residence Club Aviara and the Four Seasons Residence Club Scottsdale are two of the most highly rated timeshare resorts in the world. I haven't had the pleasure of staying at either one, but I would like to. The demand to trade into these resorts, especially during peak seasons, undoubtedly vastly exceeds the number of deposits from owners at these resorts. Because these resorts a pretty much in a class by themselevs -- in quality, purchase price, and maintenance fees -- owners buy to stay at Four Seasons, not to trade into lesser resorts.
A few people on this board have had success trading in. Do a search for Four Seasons. The best chance of success will come from submitting a request to Member Services 2 years ahead of when you want to stay, being flexible with dates, and not having your heart set on a peak season week. Then don't expect anything to happen for at least a year. Have a backup plan in case your trade request is unsuccessful.
Not all I.I. trades are this difficult. In fact, you can get instant confirmations at many resorts on
DVC's I.I. list, usually around 6-12 months out, especially if you're traveling off-season. But the best properties during the high seasons -- in other words, when you're really getting a good value for your points -- will take planning and luck.