I'm going to give you one you may not think about, the #17th at Augusta. The pros think it's easily the most difficult green to read on the course. Ben Crenshaw said that if he were to build a practice green in his yard, this would be the model. It's one of those things that won't slap you in the face, but slowly grows on you, then you totally get it. The contours are so subtle and so difficult, yet very fair. It's very hard to tell what is uphill and what is downhill. It's clearly not a severely sloped green, i.e. #5, 13, 14 etc., but it's beauty, to me, is in its subtle difficulty.