Since you live in Washington, I would say 1) Worldmark 2) Marriott 3) Vistana (mandatory resort)
Worldmark's quality is consistent, more like 3*, clean and large generally except for locations in expensive cities like the ones in Vancouver and Victoria. With more than 90 locations along the west coast, low maintenance fees and no extra reservation fees, the value proposition is the best. Inexpensive to buy in the resale market, at 10 to 20 cents a point. If you want to trade outside of Worldmark, you can use either RCI or II.
Marriott's quality is consistent and closer to 4*, many locations in US and several in Europe and Asia. If you want low entry price, you will have to buy a less expensive maintenance week and trade in II. Marriott timeshare has priority period in trading back into another Marriott and Vistana (Westin/Sheraton). If money is no object, then buy a hybrid package, i.e. points and week, from Marriott to get it closer to $7 a point, with the option to use internal trading system, i.e Destination Club (to be renamed Abound), as well as free trading in II. I don't like to only buy resale points because Marriott Vacation Club points cannot trade back into Marriott in II. Points booking is easy and very flexible in Destination Club but it is more expensive for the stay.
Vistana, i.e. Westin/Sheraton, has been bought by Marriott and is in the process of being merged. It may not change for those who buy in the resale market, unless you want to shell out more money to Marriott to bring the week into the system. Buy a resale at one of the 5 mandatory resorts, and you should be able to use Vistana internal reservation system, or trade in II.