MailChimp has one of the best APIs I’ve worked with. Authentication is easy to set up, it is fast, and has many resources to pull data from.
I’ve created a simple analytics dashboard, with focus on the email channel, using my MailChimp account. You can see charts with members by country, and top posts based on the most common email marketing metrics. The dashboard is here.
Don’t hesitate to reach out to me if you want to learn more about this!