If you know what kind of topics you find most interesting, you should put that on your list of preferences (combined with culture, location etc). If you have a weird mix like Biomedical Computing, Program Correctness, Computer Vision and you really like SAT solvers, finding out where the hotspots for those topics are can help you select a uni. I know of a few people that selected based on professors that would be available to them, and some that were purely interested in getting into any of the FAANG, that does limit your options and as a result should make your list much shorter.