My son is deciding between these two as a chemistry major. Here is what we have been able to tell and appreciate any additional thoughts:
1. Prestige-wise, while Northwestern rates higher in the US News Ranking, most people in California where we live either view Berkeley as more impressive or view them as equal. The chemistry department itself is ranked higher at Berkeley, although Northwestern is very good. ISP is viewed well within Northwestern, but doesn't seem to be known externally. Overall, leans a bit to Berkeley.
2. Research: ISP students have almost guaranteed research. It takes more effort at Berkeley, but it seems like people who really try can get it. Overall leans a bit to Northwestern.
3. Class size: Very small classes at ISP, vs. Berkeley, although upper division classes at Berkeley should also be pretty small. This one favors Northwestern.
4. Rigor/GPA impact: Both seem to have about a B average in a very competitive group of students. ISP requires a lot more depth in math and physics that might become challenging. Berkeley students might be more competitive. This one seems like a wash.
5. Grad schools admissions: This one is hard to gauge. There weren't a lot of students in chemistry going directly to grad school in the ISP data provided. They seemed to do well, but not everyone was going to a top program. Berkeley data shows almost everyone going to a top program, but the data is less comprehensive and it might be that only the people who did well are reporting their results.
6. Hand-holding: I assume Northwestern makes the student lives easier, although not sure where this will come into play. i understand College of Chemistry has more of a small school flavor within Berkeley but not sure what the examples are here either.
6. Other factors: convenience/closeness to home, weather, cost favor Berkeley.