Campaigner

Very straight-forward managing multiple mailing lists; useful and detailed analytics for email campaigns; very helpful and quick customer service (I suppose that the reason customer service reps are available so quickly is because they are not needed often, which speaks to the high quality of the software).

Because I do very time-sensitive campaigns, sometimes the test email doesn't arrive as quick as it should.

We use it for simple email blasts to our neighborhood association. We don't use it for marketing campaigns, so therefore do not have the need for some of the functionality available with Campaigner. For our needs it works.

Ease of use. It is not intuitive, and they haven't done any kind of software or GUI redesign since we started using it (6+ years ago).
Making a template should be a lot easier than it is: Creating and editing templates has a lot of old graphic (frames?) technology that makes for a frustrating experience when trying to line up text blocks with headers, footers and images.
Writing an email with attachments should be easier. Having to upload a file/image to the media library, and then importing it into your email is a lot of steps. Instead, allow a person to add a file/image to an email note in the same simple fashion as any other email client works: add a paper clip button and allow us to select the file to add to the note. That seems like it should have been done a long time ago.
Also, if you accidentally remove a person from an email list, you have to call up Campaigner support to get it fixed; you can't manually fix it yourself. Very annoying.