CC Madhya-lila 08.161 - Ujjvala-nilamani
Sri Caitanya-caritamrta
CC Madhya-lila
CC Madhya 8.161, Translation and Purport:
“"Among the gopīs of Vṛndāvana, Śrīmatī Rādhārāṇī and another gopī are considered chief. But when we compare the gopīs, it appears that Śrīmatī Rādhārāṇī is most important because Her real feature expresses the highest ecstasy of love. The ecstasy of love experienced by the other gopīs cannot be compared to that of Śrīmatī Rādhārāṇī."
This is a quotation from Śrīla Rūpa Gosvāmī’s Ujjvala-nīlamaṇi (Rādhā-prakaraṇa 3).