LGB is the closest and by far the most convenient. Small airport, pick up your rental car literally across the street, a few miles up Lakewood Blvd and then a straight shot down CA-91 to State College Blvd. SNA is your next best bet. Beyond that, ONT or LAX are distant thirds. (Fullerton native-- but it's been a while since I've driven through on a non-holiday or weekend, so won't make predictions about traffic).