It’s what is ‘better’ to you. They are very different experiences, but academically you can argue the toss.
@VickiSoCal has the most current info on St As, so I will defer to her- except to say that people seem to either really take to StAs- or they don’t.
Durham has about twice the number of students as St A’s and is a collegiate university, so you belong to a college within the University and you live in your college for most of your time there (‘living out’ in 2nd year is common, but you are part of your college all the way through).
tbh, I recommend first reviewing the course descriptions carefully to see if the differences between the programs are important to you. If the modules in one place look more interesting that is an important factor. After that, look at where you want to live for 3-4 years. Can you visit Durham during spring break?