I hope I can get some insight on these two email systems. Our organization currently uses MailChimp for almost all of our email sending, complimentary ticket offers, thank you for joining, helpful hints, etc. I build all of these manually and have to import a list and send them manually each time. We'd love to get something where automation can be done well. I've looked through the forums for suggestions and opinions of the products but didn't get any clear answers. If anyone is using WordFly or Prospect2, I'd love to hear your transparent pros and cons of the service you're using.
We use WordFly and overall I think it's a good product. Designing emails is very easy and customizable. We made the jump from the old Mail2 product to WordFly instead of Prospect2 because of cost and we also didn't think the marketing automation capabilities at the time were a good fit for us.
We send several types of triggered emails through WordFly including performance reminder, post-show thank yous, surveys, declined credit card notices for monthly gifts, etc. Prospect2 does have more features like being able to send to someone who clicked on a link but then didn't purchase, but honestly our email schedule is so dense that we didn't think it was a huge value add on for us.
I think it depends what you really need out of a system and your budgets.