I would pick Brown.
I was a graduate student at Hopkins some time ago and I taught classes and honestly, the undergrads didn’t blow me away. However, it is more competitive than it used to be, so maybe the caliber of students and the classroom vibe has improved. This also may vary according to major.
The surrounding area of Brown is nicer, IMO. It’s adjacent to downtown and the immediate neighborhood by campus is quite nice. Great architecture, nice restaurants, coffee shops, bars, etc.
Brown’s acceptance rate was about 9% this year, so I don’t think “laid back” applies. However, I think that the learning environment is more collaborative than competitive from what I know of students who have gone there and professors who teach there.
If I remember correctly, Brown has a well-regarded neuroscience program.
Have you visited both campuses? An overnight visit and/or sitting in on a class might help in making your decision.
Congrats - great choices, both!