First, run the numbers carefully, and eliminate anything that is out of your budget: http://www.finaid.org/calculators/awardletteradvanced.phtml
If you are certain that you want CS, then you need to know how difficult it would be to move from “undeclared” or “pre-physical science” to a CS major at that university. If it will be easy, then you can pick based on any factor that is important for you. If it will be hard, and you can afford both of them, then you need to choose between UCI and PSU.