If you know that you want to transfer but you don't know where, it is harder to choose classes because you don't know what will be required. The sooner you narrow down your choices, the sooner you can follow a transfer plan that shows the general education and major course that school requires.
If you are uncertain about where you will transfer, it is important before taking too many classes to talk with a counselor to plan a strategy that keeps your options open. Some students choose to start with general education courses required by the CSU or UC systems while deciding, but this is a temporary strategy.
You will also want to explore which universities offer the major that interests you since not all campuses offer all majors and that choice may help narrow your options. Visit Assist.org for majors information at CSU or UC. You many also find information about majors using the Eureka computerized exploration program in the Career Center.