They are built for different halves of the job
pgAdmin is an administration console that also shows table data. TablePlus is a data tool with no administration at all — no roles editor, no tablespaces, no configuration, no activity dashboard. If you need to grant a privilege or check what is blocking a query, TablePlus will not help and pgAdmin will. If you need to read three hundred rows and correct four of them, the reverse is closer to true.
