For CS, all 3 schools are (MORE THAN) good enough and there is really not much difference.
The decision will come down to:
(1) private or public school? If private, then the choice is between USC and NU.
(2) LA or Chicago? Pick USC/UCLA if LA is the preferred location.
(3) Any possibility of venturing into something else (other than CS)? Then NU would have an edge.