I think from a sending/tracking perspective most of the services listed here are somewhat comparable. All of us realize that delivering to inbox is a high priority and we do many of the same things to make sure your infrastructure is optimized to achieve that. In addition, most services have analytics that track your emails. Of course, I am biased on which is best.

From a broader perspective, Mailgun's focus is being a complete mail platform (sending, receiving and storing messages) and integrating email with your application vs. a sending/delivery service. A quick glance at the front pages of the websites reveals that.

I would encourage you to review the documentation of all of the services in order to make the decision of what is right for you.