im planning on applying as a cognitive science major to those 3 schools.
The major you choose doesn’t affect your chances of admission to both UCI and UCSD as they accept you into the school first. If you don’t get in for the major you chose, then they consider alternate and if you don’t get in for that they just give you undeclared. With that being said, the hardest major to get into at all three schools would probably be Computer Science and EECS at LA.
The hardest majors at UCI and UCLA would definitely be nursing! Their acceptance rates are 2-3%…