PCH by far is a better drive than the I-5 South. Here's the best route, including Big Sur, Morro Bay (Get some chowder or else). I've also made sure you don't miss out on Malibu Canyon. If you're in the area on a weekend morning one or more of us will run through it with you. Pretty much straight 405 to San Diego from there.
San Francisco, CA to San Diego, CA - Google Maps
See you soon!