Well, I can obviously speak for DC!! ;)
It agree that it should be on the top list being that it's politically a major city of the world and has a lot to offer. In the past ten years, I can say it's become more international as far as the nightlife and dining. You can enjoy authentic Ethiopian, Indian or Peruvian cuisines for cheap (I like to pretend DC is becoming like a mini NYC in the dining sense). There are also a lot of free museums, concerts and parks. This is a great site to check out free stuff in DC. http://washington.org/visiting/browse-dc/attractions/100-free-things-to-do
Not to mention that Northern Virginia and Maryland also have beautiful parks, the Pentagaon (in Arlington) and shopping malls like Tyson's Corner, Pentagon Mall, etc which are only about a 30min. metro ride away!
Ok, that's my two cents on why DC is great!! Can you tell I'm getting homesick ;)