I have considerable first hand experience with both schools. Durham is becoming a much better city than Princeton (at least from a college student’s perspective) but Princeton has the benefit of being relatively close to NYC. The work-life balance probably favors Duke but I doubt stress levels will vary significantly (pre-meds at both schools can expect to be worked hard). Princeton’s grade deflation builds resilience but can prove to be an annoyance on occasion.
Duke’s campus is bigger and definitely more buzzing (probably because it has significantly more students). Princeton’s campus lends itself to quiet contemplation. Princeton’s professors are probably the best in the country. Duke’s faculty may not have quite the same luster (although that is changing rapidly) but the sheer quality is still palpable.
If your son is incredibly serious about going into academia, I’d give Princeton a slight edge. If he wants to become a professional, it would make sense to go to Duke.