Srimati Radharani is the highest

[Bhakti Vikasa Swami]

Of all the devotees who have developed unalloyed devotional love for Krsna, the
gopis are most exalted, and out of all these exalted gopis, Srimati Radharani
is the highest. No one can excel the devotional service of Srimati Radharani.
Indeed, even Krsna cannot understand the attitude of Srimati Radharani;
therefore He took Her position and appeared as Sri Caitanya Mahaprabhu, just to
understand Her transcendental feelings.

Srila Prabhupada
The Nectar of Instruction, Text 10 Purport