I own timeshares with Marriott and Wyndham. As investments, they are not a good idea. Used for vacations, particularly with a group or a large family, they can work out well. Marriott and Wyndham have flexibility now that they both have a points based system in addition to the week system. I don't have to stay at my home resort. I don't have to stay for a whole week. I can get almost any size unit I want or need. Wyndham trades thru RCI and Marriott through II for units outside these brands.
My wife and I are going to AZ with our son and daughter-in-law. We are staying 2 nights in a Wyndham unit in Flagstaff. Then we travel to the Grand Canyon for 2 nights in a park facility. Back to Sedona in another Wyndham unit for 3 nights. The Wyndham units will be more than a room with 2 double beds. We will have a living room and kitchen in addition to the bedroom and bath. Much more comfortable for 4 adults.
You can use your points for cruises and tours, but they don't convert very well.
I like the fact that Marriott has a resale program should you ever decide to sell. The unit won't sell fast, but you will get more than if you sell it on eBay. Buyers through the Marriott resale program get the same percs as the original owners. Wyndham does not have a resale program. You can buy (or sell) the Wyndham units for basically only pennies on the dollar. One reason they are worth so little is that with Wyndham, resale buyers do not get to participate in all of the programs and percs available to the original owners. I may buy more Marriott units in the future, but I will never buy more Wyndham.
My Marriott units are in Hilton Head, Myrtle Beach and Las Vegas. My Wyndham unit is at National Harbor in Washington, DC.