It’s a steep hill for SendGrid and any other email service provider to compete against Amazon SES. If the price if your only factor you are a loser in this fight; if you cannot justify the price difference with tangible features you are also a loser.
We were looking around for an email service early this month; Amazon SES seems like the reasonable choice for us; hard to beat.
I work for JangoSMTP, a transactional email service provider. Amazon SES certainly has the lowest price out there, but as you mentioned, there are a lot of reasons to choose a service provider for transactional emails, and only one is price. If you are looking for a minimalist service for the lowest price, then the Amazon SES may make sense for you. JangoSMTP is more robust, in that it has both API and SMTP relay options, along with bounce and unsubscribe management, open and click tracking and advanced reporting (Google Analytics, logging, etc.).
From what we have learned, Amazon SES does little more than send out emails. If you have the resources to implement your own list management, campaign management, DKIM signing, reporting, etc., then it's a great choice. If you need a company to do this for you though, you'll still want to go with a service like JangoSMTP.
We were looking around for an email service early this month; Amazon SES seems like the reasonable choice for us; hard to beat.