The most excellent invocation is:
Alḥamdulillāh
and the most excellent words of remembrance are:
Lā ilāha illallāh.
The most excellent invocation is:
Praise is for Allah.
and the most excellent words of remembrance are:
There is none worthy of worship but Allah.
Reference:
At-Tirmidhi 5/462, Ibn Majah 2/1249, and Al-Hakim who graded it authentic
and Ath-Tbahabi agreed 1/503. See Al-Albani, Sahihul-Jami' As-Saghir 1/362.