LACs are among good places for undecided students. However, OP doesn’t seem to be undecided. S/he even indicated that s/he would major in either physics or biology. I don’t know how committed s/he is to STEM, but if s/he is, some universities would likely be better options than many LACs. Smaller classes in STEM, or any subject, also aren’t limited to LACs. They’re mainly the function of the size of the college relative to the size of its faculty. Caltech, for example, likely to have classes even smaller than most LACs on average. Having professors undistracted by their researches isn’t necessarily a positive either. Undergraduates do often benefit from professors’ researches, especially as they start taking more advanced classes or participating in researches in their fields.