Being new to the field of email marketing, I'm not exactly entitled to judge ActiveCampaign's services, but I can say a couple things for sure.
First, their user interface is awesome: name a feature, it's there, exactly where you expect it to be. Practically everything is wizard-guided, but in a way that doesn't become pedant the third time you use it. Or the 300th, for that matter.
Second, their support guys are very responsive, kind, and competent. Even for low-cost accounts.
Last but in no way least: Automations! As a professional software developer I always appreciate being able to customize something with code, but ActiveCampaign took this a giant step forward with their visual editor. One of the best UI's ever! By combining Automations, contact tagging, and a bit of creativity, there's really very little you can't do.