What is the best remembrance (dhikr)? What is the best supplication (du'a)?

It is authentically reported from the Prophet, peace and blessings be upon him, that "The best remembrance (dhikr) is 'La ilaha illa Allah' (There is no god but Allah), and the best supplication (du'a) is 'Alhamdulillah' (All praise is due to Allah)," because praise is an expression of gratitude to Allah, and gratitude is a reason for Allah to increase His bounty, as He, the Almighty, said: (If you are grateful, I will surely increase you [in favor]).