I run a marketing and creative agency, and we turn down any project that requires us to use Constant Contact. Like Windows, its popular because it was the first of its breed, not because it’s better.
Constant Contact uses old technology that makes the emails based on tables and old coding methods. The presence of their logo in the mail alone can trigger spam filtering on some servers. We found using a customized layout in the program to be more than a nightmare.
If you are looking for email newsletter services:
MailBuild is fantastic. You can do your own layout or they also have basic templates to choose from. The reporting feature is fantastic.
MailChimp has a silly name, but is very robust and super easy to use.