Chatfuel vs SendGrid

For transactional emails, notifications, reminders, etc, I want to make it so writers/designers can set up the emails and maintain them, and then dynamically insert fields, that I then replace when actually sending the mail from code.

I think the ability to use a basic layout template across individual email templates would make things a lot easier (think header, footer, standard typography, etc).

What is best for this? Why would you prefer Mailgun, SendGrid, Mandrill or something else?

The problem I have is we are using mailchimp and not happy. We want to switch to mailster and are curious the easiest and best way to send emails with mailster.

The most important factors for me are ease of use, tracking.

I have only had experience with mailchimp, constant concact and streamsend. So ease of use is important.