Quality support, Great performance and Amazing up time record.
If Customer Service is important in your decision making then stay away from Elastic Email. Performance is good for periods of time however we've experienced at least six major issues the past two weeks. No one picks up the phone and took over 3 hours to respond to support tickets.
We just completed a comparison of Mandrill and SendGrid here: indiemark.com/...
Ive used Send Grid for mingletrips.com. Works great. We are going to use Amazon SES since we are hosting the next app on EC2. Will give my feedback on SES.
SendGrid's API's make it so easy to integrate!