After working for years with both, I'd say that PostgreSQL is much more friendlier to the developer and more pleasant to work with. In any area: documentation, features, error messages, available SQL features, available extensions, available docs, available books.
One tiny example: I prefer to work with databases using CLI interfaces (mysql and psql).
psql CLI is a tool which is pleasant to use, has no bugs in the interface and it even gets improvements from time to time.
mysql CLI is awful to use (e.g. doesn't display long lines properly, has difficulties with history editing, etc) and looks like there wasn't a single improvement since 1996 (I'm sure there were, I just never felt the effect of such improvements).
Actually, there was a significant regression. Many many years ago, Oracle decided to drop the support for the gpl-licensed readline altogether, likely because they can't ship it with MySQL Enterprise. To this day, Percona still carries a small patch to add that functionality back, which is great because I wouldn't touch any CLI without readline.
Yep Postgres seems to have more features too for sure.
Also, a fun little limitation of the MySQL CLI is that it truncates hostnames to 100 characters - not usually a problem, but AWS database VPC hostnames easily hit that limit, and it just silently truncates rather than failing.
One tiny example: I prefer to work with databases using CLI interfaces (mysql and psql).
psql CLI is a tool which is pleasant to use, has no bugs in the interface and it even gets improvements from time to time.
mysql CLI is awful to use (e.g. doesn't display long lines properly, has difficulties with history editing, etc) and looks like there wasn't a single improvement since 1996 (I'm sure there were, I just never felt the effect of such improvements).