I agree with Geekette -- there is no "best" program. What is best for one person may not be that good for another. Many people, for example, like Worldmark and I don't doubt that it has a good program. But most of its resorts are located toward the west coast and that would not work well for me.
She gave some good suggestions as to what information that you might provide that can help us steer you in the right direction.
[Maybe, a few comments to get you started... These are some very quick quips that others may not fully accept. Call them one persons impressionistic (perhaps misguided) view of the points clubs...]
HGVC has the most uniformly high class resorts, but much more limited locations than the other point clubs.
Bluegreen is located mostly in the midwest and south east.
Worldmark is stong in the west.
With Fairfield be sure that you understand the different levels of membership. (Not being part of it, my eyes gloss over as I glance at some of the explanations. Maybe if I seriously looked at it, it would not seem so complicated.)
RCI Points is basically a grouping for "independents." It has the largest selection of resorts, but availability depends upon how many Points memberships were sold at a particular resort. At some, availability is easy, at others near impossible.
Shell Vacation Club has a fairly wide range of resorts, but some who have looked into it complain that its maintenance fees are too high. (I don't know how high that is.)