I like the ability of CC to manage the contact database, For example, the same email campaign can be sent multiple times and it will not appear in the same inbox twice. It also merges duplicate contacts. This really gives peace of mind for those worried about spamming subscribers.
Honestly, CC's best selling points is that none of the competitors are comparable.
Be extremely careful when importing contacts. CC wants to see how they actively subscribed. Sometimes it is hard to prove this when you have entered information for people you have an established relationship with, or if they verbally requested to be added. CC wants to actually see the (paper) sign-up sheet. This is unachievable for businesses/groups that have been around long enough to have established an email list based on personal relationships. Also, if the email campaign does not promote a product or solicit donations, updates on e.g. new, educational blog posts should not cause CC to initiate an investigation of practices (so long as there is a clear option to unsubsribe and the list is being managed in an ethical manner).
For instance, an email list that updates interested individuals on current events has utilized CC (and paid large sums of money to CC) for 10+ years, had an 30% open rate (twice the industry average), only had one spam report in a decade (which was from an irate individual), and does not even profit from email campaigns should not be subject to an investigation requiring long-term subscribers to op-in just because a contact database was exported, segmented in accordance to CC best practices, and then re-uploaded with the exact same contacts that were included in the original database.
After speaking to five representatives over the course of five hours, it became clear that CC does not value their most loyal customers, even if these customers exemplify best results. Given the thousands paid over the years for the account, this isn't just bad customer service -- it is also bad economics.
See my earlier comments about the drawbacks of CC.
Unfortunately, despite my experience, I still believe there is no better alternative. However, you must take some pretty gratuitous precautions in importing contacts. I understand that they are facing a lot of lawsuits regarding unsolicited emails to contact lists that are often paid for. For those of us who display best practices, this is ridiculous.