CC Ādi 4.44

taṭastha ha-iyā mane vicāra yadi kari
saba rasa haite śṛṅgāre adhika mādhurī
Word for word: 
taṭa-stha ha-iyā — becoming impartial; mane — in the mind; vicāra — consideration; yadi — if; kari — doing; saba rasa — all the mellows; haite — than; śṛṅgāre — in conjugal love; adhika — greater; mādhurī — sweetness.
Translation: 
But if we compare the sentiments in an impartial mood, we find that the conjugal sentiment is superior to all others in sweetness.
Purport: 

No one is higher or lower than anyone else in transcendental relationships with the Lord, for in the absolute realm everything is equal. But although these relationships are absolute, there are also transcendental differences between them. Thus the transcendental relationship of conjugal love is considered the highest perfection.