What is the difference between seeking forgiveness (Istighfar) and saying, "There is no god but You; glory be to You, indeed I have been of the wrongdoers," and which of them is better for relieving distress and worries?

Advice for the distressed: Frequently recite the supplication of Dhul-Nun, "There is no god but You; glory be to You! Indeed, I was among the wrongdoers," due to its merit in relieving distress. It combines monotheism with seeking forgiveness. It is also advised to strive in obedience to Allah and to be patient with people's words.