All of the above. We have been KOA members for several years and the cost pays for itself every year. The hook, of course, is that they encourage you to stay at their parks to get the discount instead of others so it's a win-win for both parties.
We have found the KOA campgrounds to be a cut above the ordinary but some are better/worse than others. You just have to try them and make a list of the ones that are good/bad for you.
We (two 80 year olds) typically stay at the same CG's as in the past and don't normally go to areas we have never been. Our adventurous spirit has flown!