From my 0L experience, this forum, and visits to NU, Northwestern prides itself on being a "different kind of law school." They praise practical experience, matriculating 95% of their 1Ls with at least a year of work experience. Also, I believe you can take at least one clicic per semester for two years. Conversely, Chicago is a very ivory tower academic style institution.
Plus NU is in the best part of Chicago located on the lake near the Magnificent Mile and within walking distance of Millenium Park, whereas Chicago is in one of if not the worst, where the SWAT team was patrolling the streets earlier this year (ok I'm being a bit dramatic, but the SWAT Team was there).
However, Chicago is definitively more prestigous producing more Big Law Attorneys, law professors, etcetera.