Neither fixed or floating is better for buyers. Both are fine and there are advantages to each. It is merely up to an individuals wants and desires in which is most logical.
A fixed week owner does not have to bother calling the resort and requesting a reservation because every year their vacation time is the same week. This is great for someone who has a set schedule for his or her own purpose. For instance anyone who skis or is a beachcomber would be an ideal candidate for fixed time.