I have one slot to fill in in the coming term. The two candidates are Functional Analysis and Complex Analysis (both on the undergraduate level). Here are some questions: 1) Which one would you pick and why? 2) What other classes in the standard B.Sc. math curriculum rely on either of these two? (E.g. Advanced Probability Theory uses many results from Functional Analysis). 3) Which one is harder in your opinion? (The question is obviously subjective but I think most people would agree that, say, Real Analysis is harder than Linear Algebra, even if they have the same amount of credits and the same prerequisites.) Any remarks are hugely appreciated.