We've seen problems from time to time with sendgrid and mailgun IPs getting blacklisted. Moved to Postmark, who are super-strict about transactional email only, and we've not had trouble since.
I've been recommending Postmark for transactional email and one of the others for newsletters.
I tried using it once. It did not seem solid. It didn’t support 2FA, and required my actual account username and password to send email from the server.
How hard can it be to send an email? Why pay $$$ for it?
For deliverability, which is pretty good on Mailchimp.
However I think that send emails out using the gmail API or the Amazon SES might be the way to go. Also depends on what you are doing, I think that those that over analyse the mail openings are getting it wrong, focusing on the wrong metrics. You should be focused on the sales metrics not be navel gazing in newsletter software. Content is king, get that right and again, focus on that, not the analytics.