So many features. Before deciding on MailChimp, I did a bunch of research on the other options. MailChimp blows the other services out of the water when it comes to features.
I was pretty pissed once we had to start paying because it was (at the time) more than we were paying for hosting which is pretty ridiculous. Then I started playing with some of the transactional services and started going through the motions of recreating all the little stuff MailChimp has. Four hours later, realized it wasn't worth it.
With that said, the cost is still pretty steep when put in the context of our total tool/service spend so we’ll be using Mandrill for everything pretty soon, we already use it for Transactional Emails. Pro Tip: use the two-factor auth app Alter-Ego and you get 10% off your MailChimp bill, every month. Security FTW.