I have used Constant Contact for several years across several clients. I send out hundreds of thousands of messages every week to professionals in the insurance field (agents and brokers) and legal field (lawyers and expert witnesses). I find the service generally good, but I have a problem with their policies.
I never used the templates provided by Constant Contact. All of my clients use their own custom designs. I find it easy to upload and manage the different designs. Constant Contact treats the design, the list of contacts to receive the mail and scheduling information as a unit. I think it would be easier if the design were saved on its own and could be associated with a list at the time it's scheduled (the system used by Endai Worldwide), but Constant Contact's architecture is easy enough to get used to.
Even though the service is technically among the best, I cannot recommend Constant Contact, unless you can tolerate a sudden, non-appealable termination of your services. Constant Contact is very strict about spam complaints. Constant Contact allows only one spam report per 1000 addreses in your list. It doesn't take too many people having a bad day to get your list banned. At that point, you can never send email to that list again. There is no flexibility on this, even if you escalate to a supervisor (I've tried).
As an example, I have a client that sends out a large number of emails to expert witnesses on a weekly basis, and has been doing so for over a year at Constant Contact. The list is very mature (it was used for about two years with another provider, prior to Constant Contact) and gets very few complaints. We recently moved a small list of a couple thousand addresses from another service to Constant Contact. The first time we sent to this list, we got a few spam complaints (not unusual when switching services) and, as explained to me by Constant Contact tech support, a single person compained directly to their ISP. This single complaint caused that entire list to get banned. Because that list is banned, we are not able to consolidate on Constant Contact as a single provider, so we will have to look elsewhere.
While Constant Contact's user interface is better than most, their deliverability is not noticeably better than other providers.
Constant Contact does not offer an autoresponder, but their report does tell you, on a link-by-link basis, the email address of any recipient that clicked on a link.
We have quite a bit of experience in e-mail marketing. We send out hundreds of thousands of messages each week to seasoned opt-in lists on behalf of numerous clients. If you are a professional firm, sending e-mails to other professionals, we can probably help you. Give us a call: 973-796-2820.