I interviewed at 3 of those 4 when I was an MS4, and the 4th one (Maryland) is the alma mater of a good friend of mine. First thing I'll say is never let anybody else rank your programs for you - base it on your own experiences there, priorities, and feel for each program.
That having been said, my personal opinions - I had strong negative reactions to Northwestern and Emory...not my style. OHSU I really enjoyed, ranked 3rd on my rank list. Maryland is an excellent IM program, can't go wrong there.