We moved over to SES a long time ago. Mandrill was basically the cheapest game in town, but their terrible service coupled with Mailchimp essentially abandoning the platform after their acquisition made us jump ship. I feel bad for anyone still using their service.
Depends on your volume. Mandril has a monthly fee and thanks to pay as you go pricing SES is cheaper up to a decent volume for a lot of startups sending just transactional email.
