Physics - Cornell > Penn > NU
Computer Science - Cornell > Penn > NU
Engineering - Cornell > NU ~ Penn (varies depending on what type of engineering)
Economics - NU > Penn > Cornell (but for business and business-related recruiting Penn > Cornell > NU)
Social life - Penn > NU > Cornell (but this is more subjective)
Location - Penn > NU >Cornell
For undergrad keep in mind that overall school standing, quality in addition to specific departmental quality matters as well as personally fit.
Overall undergrad desirability/standing: Penn > Cornell ~ NU
Yield rates (% of admits who choose the school): Penn (68%) > Cornell (53%) ~NU (53%)
Here is how cross-admits choose between these schools.