SSL doesn't make much difference at all where Usenet is concerned due to the very nature of it.
As for which is better out of retention or connections depends on your personal circumstances. If your lucky to have a VERY fast connection then more connections will "help" but anything more than 10 connections is superfluous for most users.
Again with retention if your simply after the latest "material" then most decent Usenet providers will be fine but if you want something less common then the higher the retention then the more chance you have of being able to download it.
Newsdemon is absolutely fine, and cheap, for 99% of people. Giganews is more suitable to the heavy/really involved Usenet user.