Hi! Congrats on having some great choices! I'm a senior studying physics at Harvard, so that's the perspective I'm coming at this from. I just applied to PhD programs this year. I do primarily astrophysics theory research but I have worked in particle theory before too.
Better student vibes
elaborate on this?
Expensive (low aid? not sure yet)
you should try to resolve this ASAP, could be the most important factor of the decision making process.
Larger school so more courses and rigor possible
I think most high schoolers underrate this, especially if you're thinking of grad school. though not necessary, it's nice to have some graduate coursework under your belt going into phd admission and that's usually very hard at a LAC. even otherwise, having more electives is nice for figuring out what kind of physics you want to do in the future.
it sounds like you are considering at least to some extent graduate school? if so, while it's cool that Reed has a student-run reactor, Chicago's particle resources are orders of magnitude more useful both for doing undergraduate research and connecting to folks in the field. At Reed, the best you'll be able to do is REUs over the summers. Those are fine and do work but it's not as flexible.