University of Vermont vs Brandeis: which has smaller class sizes?

Brandeis will usually feel smaller in the classroom. It is a much smaller university overall, and that tends to show up in discussion-based courses, seminar-style classes, and earlier access to professors who know students personally. The University of Vermont can still offer small classes, especially once you move into your major, but intro courses are more likely to feel bigger.

If you care most about being known by name early on, Brandeis is more aligned with that experience. Intro classes there can still be larger, especially in popular departments, but the scale is usually more manageable than at a larger public university.

UVM fits students who want the resources and energy of a bigger campus and are okay with some larger lecture classes at the start. In many majors, the first-year and sophomore-level classes can be noticeably bigger, particularly in common prerequisite subjects. By junior and senior year, classes often shrink a lot, so students who stay engaged in their department can still build close faculty relationships.

So for your specific priority, Brandeis is the clearer match. UVM is not unusually impersonal, but it is more likely to have that large-university feel in introductory coursework, while Brandeis more consistently offers the smaller-class environment you seem to be looking for.