My parents have one through RCI. I would recommend getting one that is reasonably closeby, within a couple hours of your home. Don't buy one in Hawaii or some place that's hard to get to because you want to be able to use it every year rather than give it away. My parents trade their week and usually go someplace else so make sure your week that you pick is during the "peak" season wherever you chose, so pick during the ski season if you get one in the mountains or don't get one during hurricane season if you get one in Florida or someplace like that.
Watch out for the maintenance fees and other hidden fees. Also never accept their first offer, or their second offer, tell them all the way through that you don't want one, the offer will get better and better as they pass you on to other "closers".