Unless there are some specific resorts that you like in RCI Points, HGVC or Fairfield, I think you may be better off with WorldMark or Bluegreen. You should include those systems into your selection mix. WorldMark for the west coast and Bluegreen for the East Coast
RCI Points has the most number of resorts from which you can reserve partial week stays. And, they have a nice program in Points for Deposit where you can get more points by depositing RCI weeks into your account. The problem with RCI points is that the fees are getting out of control.
HGVC has some nice resorts and they have great trading power in RCI. It's good for use in SFX for high quality exchanges. But, they don't exchange with II which is where most of the highest quality timeshares exist. The entry cost and maintenance fees are high.
Fairfield has a lot of nice resorts. And, the upfront costs to buy into Fairfield are very low. These two reasons by themselves are a good reason to buy into Fairfield. However, it's a complex system that can be confusing at times. And, their maintenance fees are a bit high.
WorldMark and Bluegreen have moderate upfront costs (higher than Fairfield, but lower than HGVC), but their maintenace fees are low. This makes your ongoing costs for usage and exchange very attractive. And, both allow you to exchange through all exchange companies including II, SFX, DAE, RCI, etc. WorldMark has the best online reservation system. Bluegreen has the best bonus time program with very cheap rentals to owners less than 45-days out.
I don't think you can go wrong with any of these point systems. The most important decision is which resorts do you like the most and which ones will you most likely use. When you answer that question, it will lead you naturally to one system over another.