They all have their challenges, and it's interesting to see how other people perceive the courses as far as difficulty. Blue Valley is difficult because it's just a monster of a course. Cliff Drive's wooded holes are rough around the edges, and a couple of the open holes have enticing lines that can cause one to flirt with going OB. I don't have a real big arm, so I would rank WYCO among the more difficult courses in town.
I consider myself to be at a playing level somewhere between intermediate and advanced, and typically have my best rounds at Rosedale (up top), Swope, and Water Works when those courses are not completely stretched out.