I think if you're starting a project the amount of "gotcha" type stuff you'll hit in MySQL/Maria if you aren't already familiar with it is pretty significant compared to PostgreSQL. PostgreSQL is also less fragmented, which seems to be an increasing issue with the MySQL family.
But if you're already pretty used to MySQL and it's working fine in your project already, I would only switch to PostgreSQL if you think specific features would be very worthwhile.
It might be worth comparing features. I have a project that benefits enormously in terms of reduced complexity from the PostgreSQL array types, but that's somewhat rare I think.
Other things that might be useful if you have special/specific needs are PostGIS, table inheritance (not really a huge thing), and foreign data wrappers.
But really you shouldn't switch because you "might" need one of them.
But if you're already pretty used to MySQL and it's working fine in your project already, I would only switch to PostgreSQL if you think specific features would be very worthwhile.
It might be worth comparing features. I have a project that benefits enormously in terms of reduced complexity from the PostgreSQL array types, but that's somewhat rare I think.
Other things that might be useful if you have special/specific needs are PostGIS, table inheritance (not really a huge thing), and foreign data wrappers.
But really you shouldn't switch because you "might" need one of them.