Any song which describes the pastimes of Radha and Kṛṣṇa is the best song. In conditional life, the soul is captivated by sex. All fictions – dramas and novels – and material songs describe love between men and women. Since people are so attracted to this kind of literature, Kṛṣṇa appeared in this material world and displayed His transcendental loving affairs with the gopis. There is an immense literature dealing with the transactions between the gopis and Kṛṣṇa, and anyone who takes shelter of this literature or of the stories about Radha and Kṛṣṇa can enjoy actual happiness. In Srimad-Bhagavatam (10.33.36) it is said that the Lord displayed His pastimes in Vrndavana in order to reveal His actual life. Any intelligent person who tries to understand the pastimes of Radha and Kṛṣṇa is most fortunate. The songs that tell of those pastimes are the greatest songs in the world.
Source: A.C. Bhaktivedanta Swami Prabhupada (2012 edition), “Teachings of Lord Caitanya, The Golden Avatara”, Page 382