I'm going down to San Diego from Oakland and wanted to know which is cheaper overall?

I'm going down to San Diego from Oakland and wanted to know which way save money. Is it cheaper to fly down there and reserve a rental car or should I rent a car over here in Oakland and drive down there. Just wanted everyones thoughts. P.S. I've driven down there and don't mind the drive at all and I will be going for about 5 days