When it comes to two schools so similar (they’re even the only 2 boarding schools with about 800 students), the main differences you need to look at are quite subtle—surrounding area, campus structure, % day students, etc. I’d also suggest you peruse the course catalogues and extracurricular offerings of each school just to see which fit better with your child.
Anyways, I’m a current Lawrenceville student and I’ve posted a lot of information on this board about my experience (including stuff pertinent to your concerns). Feel free to peruse my profile, or ask any specific questions if need be. Good luck—you have two great choices.