I don't care about Mandrill (who uses it, anyway), but deeply concerned if I should expect same quality, incident response and attitude to customers from parent company — Mailchimp.
We've been on Mailgun for 5 years and they've been very reliable. We almost switched to Mandrill, thinking it was better for 'transactional' type emails but now I'm glad we did not! Their customer service is always responsive, too.
AWS SES doesn't have things like reporting, bounce handling etc. out of the box - you need to set up all of that yourself (or at least you did when I last looked at it a few years ago).
This was all still true ~6 months ago. Compared to Mailchimp and friends, SES is _very_ low level.
The other things I found really frustrating about SES were: templates had to be defined inline in a JSON file and then sent to SES via the AWS CLI. So, since there's is no online/visual editor, copy changes and the like required a developer to rebuild/sanitize/minify the template source and then update it via the AWS CLI.
It also took _way_ longer than it should have to have our rate limit bumped up to a reasonable level. IIRC, it took ~one week for my request to be processed (after submitting proof that we owned the domain, etc.) and it was only after a fit on twitter that AWS Support followed up with me and escalated the issue.
