Here are the top ones based (of the ones I’ve seen) based on how I feel today and not necessarily in rank order (but generally in rank order):
Larger (to midsize) schools: Cambridge (UK), Oxford (UK), Princeton, Yale, William and Mary, Colorado, West Point, Indiana University, Chicago, Berkeley, Stanford, UVA, Dartmouth, Duke.
Smaller schools: Richmond, Swarthmore, Washington and Lee, Sewanee, Vassar, Kenyon, Mount Holyoke, Sweet Briar, Colgate, Union, Bryn Mawr (I haven’t seen some that get noted such as Bucknell, Furman, etc.)
I like to visit campuses, but it is difficult to evaluate them when the weather, time of year, and time elapsed since the visit may play a factor. I broke it into larger and smaller schools since it is tough to compare them. Larger schools often some more impressive buildings and spaces, but sometimes have areas that are not nearly as nice (e.g. medical centers, etc.)