Requesting a compare/contrast (similarities? differences?) from someone with experience at both schools
You can start with the CC Super Match: http://www.collegeconfidential.com/college_search/
None of my kids wanted to be golden domers - so can’t contrast attending on a personal level - but I have visited both. NU is on Lake Michigan, close to Evanston & great restaurants with Chicago @ 1 hr away on mass transit. ND is in South Bend - and surrounded by Indiana… 
Full Disclosure: I have 2 NU alums - Go Cats!
Full Disclosure #2 - I CAN verify that ND players are much nicer than U of IL players after losing to my kids NU teams 
Hopefully someone will stop by to post more specific info for you - Good Luck with the decision.
I think you will have a hard time finding someone with experience at both schools. From what I’ve seen, though, the schools have very different vibes. (My D is a rising sophomore at ND and we have visited NU.) ND has no Greek life, and has a dorm-based residential system where most kids stay in the same dorm every year. Most kids stay on campus at least the first 3 years. Lots of school spirit at ND, particularly around football season. Lots of emphasis on community service there as well. Chicago is not that far away - train takes about an hour and a half. My D says the atmosphere is collaborative.
Can’t speak to NU, but I know it’s a fine school. (My brother went there years ago.) I think you need to visit both schools to see if either is a fit. Good luck!