There's very few times that you'd ever get from SD to LA via hwy 5 (the most direct way) without hitting a good bit of traffic. The coast road doesn't avoid it very well and passes through so many high population towns/cities that there's not much hope in having an enjoyable ride that way either.
Depends on how much time you can devote to just being out there riding of course, but here is the route I'm doing next week - gets me from SD to North of LA without ever using a congested freeway. 330 miles instead of the 130 it would take going direct, but that's the whole point!
I'm doing the ride with the specific challenge/purpose of getting up there without ever touching tire to a freeway, but given that you aren't restricting yourself that way, you could shorten/speed the ride up a bit - once you're out East, there isn't nearly as much traffic.