SendGrid automatically adds click tracking and opened email statistics. Also, god forbid you actually try to use the Amazon SDK for PHP. Two days I'll never get back. Additionally, I was unable to get Amazon to verify my domain so that I could even send emails through their SMTP server.
I don't think SES originally supported SMTP, which meant it was harder to use and I couldn't relay through a local Postfix server. I think they fixed that, but I had already chosen SendGrid by then and I've been pretty happy with the choice.
I use mailgun partly because of recommendations from other HNers, and partly because currently my usage puts me in their free tier, which SES doesn't have.