In terms of academics I’d definitely say Princeton if you’re leaning towards STEM/Economics. However, I personally prefer the collaborative and slightly more laid-back vibe of Yale in comparison to Princeton, the latter of which is notoriously competitive and rigorous.
I would definitely be very split between the two if I somehow got accepted to both, as I’m sure most would. However, it’s best not to get overconfident - you should only worry about this if you’ve somehow been accepted to both!
As a native New Yorker, I’m always interested in how easy it is to get to midtown Manhattan without driving. Princeton and Yale are equidistant by train, but Yale has a slight edge in that you don’t have to switch trains.
If someone were lucky enough to be admitted to both Princeton and Yale, take a look at the curriculum in programs of interest. Just keep in mind that whatever programs both schools offer will be top-notch.
Honestly, I would visit both and, assuming there won’t be a large difference in cost, choose the one that feels more like home. They’re both great – but they are adequately different in setting/culture/location that most kids will choose a favorite after spending a little time at both schools.