Silicon Valley feeder school rankings (adjusted for school size):
http://www.siliconbeat.com/2013/12/18/silicon-valleys-to-10-feeder-colleges-stanford-yes-but-harvey-mudd/
- Harvey Mudd
- Stanford
- Massachusetts Institute of Technology
- Yale University **5. Duke University**
- Dartmouth College
- Princeton University
- Harvard University
- Brown University
- University of California, Berkeley
I think Duke is pretty well represented in Silicon Valley. 
Actually, double majoring in Pratt is quite easy if you choose two Pratt majors – they basically just change the requirements to take more intro/intermediate level courses and fewer electives for each and the total course requirement is almost identical. If you choose a Trinity major as your second, though, certainly that requires more planning. It’s pretty popular to double major overall at Duke and I knew many who did Biomedical Engineering and Economics (finance is a minor only) and got great opportunities coming out of that. I did biomedical engineering major with a Trinity minor pretty easily. There are even a few crazy people who TRIPLE major in engineering (and graduate in four years), so it can be done. Comp sci + econ/poli sci shouldn’t be a problem honestly – it will just severely reduce the number of electives you can take which is the potential downside, but is doable in four years certainly. Having AP credits coming in would be advised though or else overloading/summer school might be required to get it done in 4 years (might have to overload a semester or two regardless, but I don’t know the curriculum requirements on those majors THAT well. You can find them on their dept websites).
I’d say Duke, Dartmouth, and Penn are pretty comparable though in your criteria. I’d go based on where you think the student would be happiest. Good luck.