One massive advantage of pgtestdb compared to using dockertest on its own is that it handles running migrations for you in a very efficient way that amortizes the cost to zero as the number of tests trends to infinity. This should be much faster than naively creating a new database and re-running the migrations for each test.

I happen to recommend using docker-compose over dockertest out of some slight personal preference that is one part separation of concerns (it's weird to me to have the test code handle the state of the postgres container), one part developer-experience related (it's nice for devs to be able to easily manage their postgres server instance with existing docker tools outside of golang code), one part infra related (it's nice to be able to use any method to provide and manage the postgres server, particularly in CI), and one part totally arbitrary.