Congratulations on all of your offers! i think you have some great options. If I were you, I would go to either Cornell or CMU, not to mention that UCLA and UT Austin are both well-reputed schools. You shouldn't get too caught up with the ranking, as there are many other things to consider--finding the right advisor, funding availability, etc. Given that public schools like UCLA tend to have far more students than private schools, one of the advantages of going to private schools (Cornell & CMU) is a favorable student to faculty ration.
Although SoCal is a pretty awesome place to live, living in LA, particularly in the neighborhood of UCLA, could be very expensive. I'm currently living in a one-bedroom apartment near UCLA and my rent is $1510 per month. You can probably find cheaper apartments but I think you would have to pay at least 1250 for one-bedroom.