I used Navicat until I finally decided to try M-x sql-postgres in conjunction with a SQL Mode 'scratch' buffer from which I can simply C-c C-c.
I'm not sure about Sequel Pro, but being able to [reverse] incremental search on \d and \dt is a blessing.
If for some reason you want to eyeball sample data for a table with a ton of columns that won't fit in one screen, then a GUI's resizable columns are nice. But usually I just type of the columns of interest — us programmers are usually good typists.
I am a huge fan of Postgres, it's never let me down. But data exploration, ad hoc querying and such is a pain in psql. These tools are badly needed.