Masters/PhD programs in the US will be looking at your body of work in your subject and possibly test scores (you don’t say what field, but many programs require standardized testing such as the GRE, GMAT and so on. I won’t say that it doesn’t matter at all which uni you go to- but any solid uni that is strong in your subject will be just fine.
Depending on your field you may want to consider how you use your summers- most American students aiming for competitive post-grad programs will be spending their summers doing something related to their field. For example, my final year undergrad is currently applying to STEM PhD programs, having done full time (paid) research every summer of undergrad, resulting in several publications; a friend of hers applying to a Humanities Masters program has spent the summers working in the field, and so on.