Flex Subs VS Membership

So we are looking at the value of Flex Pass versus a Membership style program and I was wondering if there was any pros and cons the group could assist with.  We have a great deal of unredeemed Flex Passes every season and these subscribers tend not to want to renew as they have "lost money".

Any thoughts would be a great help in finding the best way to bring in the new subscriber with a program that works for flexibility, but allows for limited loss on the part of the patron.