Like any other "sold out" DVC resort, there are usually points available to purchase. Sometimes there is a wait list to get exactly what you want. As far as I know, only GFV and GCV have been closed to wait lists.
Sold out, minimums, incentives, change when needed to make sales so don't think that they won't. Plus DVD/DVC is under new management so there is another wrinkle.
You should look for Use Years that fit your travel schedule, and don't worry about the "most popular". The chart that @Bing Showei pointed to gives the various UY breakout, but keep in mind that Disney controls that percentage. People don't "make up" a UY when they purchase...Disney has a certain amount of point available for each UY that they set. So it's really not most popular, but what does Disney assign the most to. In any event, if you are selecting a UY, you want one that fits your travel calendar.
If you feel that you will travel mostly during the summer, for example, you don't want an August or September UY because if you have to cancel a trip you would only have a few weeks to use the points or lose them.