Introduction to Econometrics
Very informative class. Take it with Jimmy Roberts if you can -- he's very engaging, and a really good professor. I learned a lot from him.
If you have a background in stats, not nearly as hard as people say
Really great class to learn how to use statistical tools (particularly regression analysis) to . Professor is amazing and really helps you understand the logic behind the statistics rather than just plugging and chugging into formulas.
The most difficult of the econ core classes without a doubt. Tests and problem sets are all brutal and graded pretty harshly. Roberts is slightly easier than Duncan but really does not matter. Although it is super hard it definitely you learn a lot of practical applications.