What are the most busted cards in Agricola?
Field Watchman, Head of the Family, and Braggart.

In statistics gathered from about 2000 games that used drafting, these occupations were picked on average earliest by the player who won the game.  See this forum post for the full details, and a list of the first chosen minor improvements too.

Edit: It turns out that several occupations are not included in these results as they were voted too overpowered by the game participants.  These are:


Ratcatcher
Taster
Chamberlain
Lover
Wet Nurse