Edit: Oops, I thought you were looking for a company which provides the infrastructure and not the full service.
I like Sendgrid. Besides transactional email, they introduced marketing campaigns a while ago, we use them for both. Deliverability is top notch but marketing features are still lacking compared to e.g. Mailchimp (which caters more to the non technical user) but they are continuously improving and even reach out to customers to get more details about their feedback.