Salesforce.com cases - we use Salesforce.com as our CRM and it is the support system of record for our company's other major product line (our enterprise solution). Salesforce.com cases is more flexible than Zendesk, and therefore ultimately more powerful, but Zendesk is easier to use and manage on-going. The biggest difference is end-user cost and the ease of access for users. ZenDesk does not charge for for end-user access, and has much simpler single sign-on. Another difference is that with Salesforce.com, you need to buy a separate community application like Jive or Lithium and we wanted an integrated application.
Jive - at the time, Jive was our company's customer community platform. Jive is a community only product. The absence of integration of support and self-service was an issue. It was harder to make the SSO work. Jive was far more complex – powerful, automation of subscriptions etc. deeper – but harder to use.