The best remembrance is La ilaha illallah and the best supplication is Alhamdulillah

It is narrated from Sayyiduna Jabir bin Abdullah (may Allah be pleased with them both) that he said: I heard the Messenger of Allah (peace and blessings be upon him) say: "The best remembrance is 'La ilaha illallah' (There is no god but Allah), and the best supplication is 'Al-hamdu lillah' (All praise is for Allah)."
This hadith has a sahih chain (sahih al-isnad), but the two Shaykhs did not record it.

It is narrated from Sayyiduna Abdullah bin Amr (may Allah be pleased with them both) that the Messenger of Allah (peace and blessings be upon him) said: "Whoever on the face of the earth says these words: 'La ilaha illallah, wallahu akbar, wa subhan Allah, wal-hamdu lillah, wa la hawla wa la quwwata illa billah' (There is no god but Allah, Allah is the Greatest, glorified is Allah, all praise is for Allah, and without the help of Allah there is neither strength to turn away from evil nor power to do good), his sins are wiped away, even if they are more than the foam of the sea."
Shu'bah narrated it from Abu Balj Yahya bin Abi Sulaym and reported it as mawquf (a statement of the Companion).

It is narrated from Sayyiduna Abdullah bin Amr (may Allah be pleased with them both) (through another chain) that he said: Whoever says these words: 'La ilaha illallah, wallahu akbar, wal-hamdu lillah, wa subhan Allahi kathira, wa la hawla wa la quwwata illa billah' (There is no god but Allah, Allah is the Greatest, all praise is for Allah, I glorify Allah abundantly, and without the enabling of Allah there is neither strength to avoid evil nor power to do good), his sins are forgiven, even if they are more than the foam of the sea.
The (previous marfu') hadith of Hatim bin Abi Saghirah is sahih on the condition of Imam Muslim, because such an addition from a trustworthy narrator like him is accepted.