NU (Northwestern) is definitely a peer school to Penn. I love NU (which used to go by NWU back in the day), and I would certainly choose it over Penn if I were you. Chicago is a wonderful city (I used to live there and had friends and NU med and law), and NU law is in one of the most beautiful parts of the city. The answer to you question depends a little on where you want to work. But NU has an absolutely stellar reputation in the mid-West (among non-lawyers even better than Chicago and certainly better than Penn and NYU), and I think it's at least as strong as the others out West.
Go to NU, and you will never look back!