Here is some interesting information about Worldmark, RCI and II. Worldmark contracts with RCI as their main exchange company. This allows their owners a simple place to exchange their Worldmark credits for a week at a Worldmark Timeshare Resort. This is actually a really great deal!
Before Trendwest sold to Wyndham, they used Interval International (www.intervalworld.com) as their main exchange company. Both are fantastic companies to help you maximize your Worldmark timeshare.