I have experience owning both Deeds and Collections. In some programs (like Worldmark), you can only buy Collections. But in Some (like Hilton and Marriott), there are owners who own Deeds and Collections.
In this video, I will describe the difference and why Timeshare companies are moving to collections (It is best for them). In my opinion collections are why there are shortages. Collections allow more people access to high demand areas that if everything were deeded.