I am always left with a weird sense of "what?" when I run into something MySQL does that I wasn't expecting. I find MariaDB to do even more weird optimizations that have led to some long debug sessions to find out what it was doing that caused the problem.

I agree with you on PostgreSQL. I think the whole reason most don't use it is because their provider doesn't support/install it by default or the "legacy" system was designed with MySQL because it was already installed.