Before being acquired, SG's support was fantastic. There are also various oddities that have cropped up, such as how they're currently hitting our webhook endpoint with the same event every 20 seconds for the past 8 days (a similar problem occurred last year too). They also seem to have suffered some dings to their IP reputation in numerous places due to, I assume, this: https://krebsonsecurity.com/2020/08/sendgrid-under-siege-fro... .. I continue to encounter numerous systems that flat out refuse any email from any IP I can muster at Sendgrid and we have a bunch on different subnets. So anyone who works at Red Hat, Packt, Akqa, Zendesk, etc.. they're not getting our mail.
We use Postmark as a fallback for users when we get the inevitable error messages back, and they have been pretty good, although I find their API a little too slow to move everything over to them and SG has a fantastic "delayed send" feature which is a must for deliverability to iCloud addresses.
Pragmatically I prefer Sendgrid, but Postmark is very good and feels somewhat more wholesome to use, particularly if your levels are low. I'd use Postmark for the same reason I'd rather use a local bakery than buy presliced at a supermarket.