Simplicity is the hallmark of a great Customer Relationship Management system. Put fancy features lists, bells and whistles to one side because a CRM only needs to be two things: easy to use and easy for external systems to talk to.
That’s not such an easy thing to answer. Let us explain why. I was at Museums and the Web 2015, commiserating with staff from a few small museums who didn't have a way to sell tickets online. A speaker mentioned that their (major) museum sold tickets using Tessitura. The person next to me (from a small art museum with no ticketing) asked me how to spell it as she wrote it down. It struck me how much museums rely on each other’s technology choices, and how easily such reliance is formed.