What is really important for me is a high-quality and fast support. They have it. Always quick and very helpful, so I can't say anything else but the support is first-class! If you, guys, find it important, than the RS Joomla team is meant for you.
Secondly, the component is also great, for me it does 3 things under one roof:
I can sell memberships with a lot of options. Great!
I can sell files. It serves as a document seller.
I can sell online tests by restricting the particular url so that noone but the subscribers can have access to it / them.
The payment by PayPal is quick and stable so it fulfills all my requirements. It is also true that I have not tested or tried other 3rd party membership components out there, but that one was the first I used and I think I stick to it because it has everything I want.