It was Lord Śiva who said, “I do not know the truth about Kṛṣṇa, but a devotee of Lord Kṛṣṇa knows all the truth. Out of all the devotees of Lord Kṛṣṇa, Prahlāda is the greatest.”
Above Prahlāda, the Pāṇḍavas are supposedly more advanced. Above the Pāṇḍavas are the members of the Yadu dynasty, who are even more advanced. In the Yadu dynasty, Uddhava is the furthest advanced, and above Uddhava are the damsels of Vraja-dhāma, the gopīs themselves.

In the Bṛhad-vāmana Purāṇa, Lord Brahmā tells Bhṛgu:

ṣaṣṭi-varṣa-sahasrāṇi mayā taptaṁ tapaḥ purā
nanda-gopa-vraja-strīṇāṁ pāda-reṇūpalabdhaye
“I underwent meditation and austerities for sixty thousand years just to understand the dust of the lotus feet of the gopīs. Still, I could not understand it. To say nothing of me, even Lord Śiva, Lord Śeṣa and the goddess of fortune, Lakṣmī, could not understand it.”

In the Ādi Purāṇa the Supreme Personality of Godhead Himself says:

na tathā me priyatamo brahmā rudraś ca pārthiva
na ca lakṣmīr na cātmā ca yathā gopī-jano mama
“Lord Brahmā, Lord Śiva, the goddess of fortune and even My own self are not as dear to Me as the gopīs.” Of all the gopīs, Śrīmatī Rādhārāṇī is the topmost.
(Sri Caitanya Caritamrta------2:8:246-------purport).