I like that SpamTitan Cloud is stable and requires little maintenance. SpamTitan support is responsive and knowledgeable. Cost is a good value and SpanTitan's pricing structure allows for use with multiple domains to maximize licensing. New email addresses are automatically learned to ease administration and automate licensing needs. SpamTitan has solid reporting that meets mu needs and user self maintenance works well.
My company has used the SpamTitan Cloud solution for approximately 2 years without experiencing noticeable technical issues or downtime. I occasionally need to add a white list entry or release emails that are not SPAM. The end users get a daily email to allow them to identify emails caught in their SPAM filter and decide how the application should handle them. The licensing count is not tied to a specific domain which is attractive if you support multiple domains or are an MSP.