BME '02:
First of all, congratulations on having a wonderful choice! Both Wash U and Duke are great schools, and as I'm sure others have told you by now, you really can't go wrong with either one.
Second of all, as a first-year MST student at Wash U, I'll try to cut the recruitment pitch to a minimum. I was faced with the same choice last year--ultimately, I was deciding with Cornell, Duke and Wash U. I'm not sure if I can really tell you the impressions I got from the schools. I suppose I tell you some obvious things, but I'm sure you already know which programs are strong in their research programs and what the medical school is like. For me, overall, it came down to the gut feeling I had about the school. All of these top schools, and certainly all the schools you mentioned, will give you a great education. Since you are the one who will be making the most of it and you are the one who will be living in that city and with the same people for 7-8 years, though, you have be sure that the environment the school provides is your ideal environment.
For me, it came down to making sure I had the right environment. I was dazzled by Manhattan and Cornell's PBL, and really impressed by Duke's 1-year-pre-clinical and Sal Pizzo. I was also very impressed by Yale's P/F system, and hardly could avoid being in awe of names like Hopkins or Harvard. But when it came down to making the decision of where to spend all these important years of my life and where I wanted to start my career, I knew I had to choose a place that gave the most support, had people I could "click" with, and had an environment that I felt comfortable in. For me, Wash U was the perfect place. I thought St. Louis might not be the best place to live, coming from the west coast myself, but it really is not bad at all. The school itself is fantastic, my classmates are wonderful, and I am very happy I made the choice I did.
That said, perhaps the choice will be different for you. I certainly hope you come to Wash U., but of course, for each person, the fit may be different. So I advise you, as probably everybody else does (sorry if this is just really repetitious to you, as I know you've been on this board for a while receiving as well as giving advice), to look around, ask lots of questions of students-and most importantly, ask yourself if this is where you belong. Go for revisits if you can. Talk to more students if possible.
Let me know if you have any more questions. Good luck with your decision!
--energy_girl