Bhagvad Gita Lesson Series #1

No living entity, including Brahma, Lord Shiva or Narayana, can possess opulances as fully as krishna.
Therefore it is concluded in 'Brahma-Smita' by Lord Brahma himself that Lord Krishna is the Supreme Personality of Godhead.

Sources:
Book: Bhagvad Gita As It Is
Author: His divime grace A.C.Bhaktivedanta Swami Prabhupada.
Pg no. 67