Everyone has their favorite membership site or suite.
We also know that even the ones we love have one or two things we wish they did, that they don't.
At the same time, reality is that once you invest time into learning one, it's pretty rare that you want to switch...you've worked the kinks out of the one you own.
Based on what you're using now and what you've seen...what would the perfect or ideal membership site, script or plugin do?
Do you already own the best that you could buy?
Maybe a way to fill in your post might be what are the essentials..."if it doesn't have _______, it's a dealbreaker.