It’s an old saw that undergrad teaching is better at smaller unis and LACs than it is at large, research universities. I don’t buy into that. I have substantial first-hand experience (although some is dated) at 4 of the 6 “so-called” super brand unis–all large major research universities. For example at Berkeley, in my time there in the 70s and 80s, Nobelists and soon to be Nobelists (Czeslaw Milosz and Luis and Walter Alvarez) regularly taught UGs, and post 2010 Saul Perlmutter and Alex Filippenko were still teaching UGs, and those are just the cases I know of personally. But at Berkeley, Harvard, Stanford, and Cambridge I was often both delighted and surprised at the accessibility of distinguished senior faculty to all students. Also at MIT the line between UG and Grad is often erased.
At Berkeley there was its own old saw: better to sit 100 feet from genius than to sit 10 feet from mediocrity.