Years ago we started with AWS SES. The pricing was amazing but there was no useful customer service outlet. If you were sending via a blacklisted IP it could be weeks before you we're seeing inboxes reliability again. It wasn't uncommon for us to devote 20+ man hours per week in dealing with email issues while using AWS.
Next we moved to MailGun. This was a HUGE improvement, however we were having to request to be moved to 'non-blacklisted' ip's on a regular basis. The pricing was great, but we were still having to invest too many hours dealing with email problems. Mostly fielding 'here is why your emails went to the spam filter, or why they never showed up' questions from our customers. You shouldn't need a template explaining to your customers why emails are showing up in spam boxes!
To be fair, MailGun was fairly new at this point but they were VERY responsive. IP's that had been blacklisted did not stay that way for long.
Lastly we moved to PostmarkApp. They were by far the most expensive ($1.50 per 1000 emails) but I only now even think of emails maybe once or twice per month. Emails just get through, no spam lists, no outages, no carrier blocks, it's amazing. Also, if you do send with enough volume you can drastically reduce the price. I believe we pay about $0.25 per thousand emails now that we purchase 5 million at a time.
They could triple their price and I would eat the costs.
I'm not affiliated with anyone above.