Your child will have a very different experience at each of these and will not be the same applicant to college from each. Neither is better but one may be better for your child. Think about how your child will develop as a student and person at each.
For academics, consider both what is offered and how it is taught.
What does your child do outside of classes? Sports? Robotics? Music? What does that require of your family in terms of time and resources? Are there requirements for EC at either that will be challenging?
L’ville has kids from all over the world while any day school is limited by its geography. Does that matter? Likewise, L’ville may have considered more than academics in its admissions process, so your kid is more likely to have classmates who are exceptional athletes, musicians, dancers, etc. Does that appeal?
Being a boarder is great for some kids and not so great for others. Where are you on this?
I really wouldn’t be focusing on “support for STEM kids” without first considering which environment was going to help my kid be his best self. These are really different options, each exceptional in its own way.