Like Dimitri Fontaine says early in the Mastering PostgreSQL in Application Development book mentioned elsewhere in this thread, psql is really powerful. From the \d meta commands to inspect anything and everything in the database, to the variable substitution, nothing beats editing sql in your preferred editor and hitting \i my_query.sql in psql to run it. You can also nest additional \i my_other_query.sql commands inside the files you run with \i, which I've found really useful for repeatedly dropping / installing test tables / views, or setting up test data, before running the query I'm actually interested in. Take the time to customize it by adding a few lines to your .psqlrc file, like \x auto, and \timing and it becomes very usable very quickly.
I used psql for a number of years, then joined a new company where DataGrip was the norm. I gave DataGrip an honest try to see what I might be missing from a GUI SQL client. After a year of using it exclusively, I slowly found myself migrating back to psql and can honestly say I don't miss anything.
But it's also possible I just haven't tried the right GUI client yet. Anyway, I hope you find the PostgreSQL client that works for you!
It's also available as a standalone product (DataGrip)
But last time I used Eclipse it was about five years ago, so things may have changed.