Ask HN: What is your preferred ESP in terms of deliverability?

HN turned me on to Postmark for transactional emailing and I haven't looked back since then. So, I'm curious to know what the best Email Service Providers are for marketing email campaigns in terms of deliverability.

I have experience using:

* MailChimp * Constant Contact * Hubspot * Autopilot

and I haven't really found one that gets it right as far as B2B deliverability goes.