Which character(s) represent the harshest critique in The Canterbury Tales?

Chaucer has a number of satirical targets in mind in The Canterbury Tales, but arguably the most important is the Church. In this deeply religious age, the Church was a powerful institution, both temporally and spiritually, and formed the basis of most people's lives. Yet the medieval Church was also notoriously corrupt, an almost inevitable by-product of its phenomenal wealth and power.
Chaucer's satire of the Church's worldliness and corruption is gently mocking rather than scathing. Nonetheless, his portrayal of the Prioress is quietly withering in its own little way. As the head of an order of nuns, the Prioress might be expected to show signs of holiness and devotion. Indeed, she wears a large pendant that says "Amor Vincit Omnia," which is the Latin for "Love Conquers All," the ultimate Christian message.
Yet the Prioress is a large, well-fed woman, whose ample girth, combined with her expensive clothes and jewelry, indicate a deep love of worldly pleasures. The Prioress symbolizes Chaucer's critical opinion of the medieval Church, which though outwardly devout and holy, has in actual fact been thoroughly corrupted by the pleasures of this world.