As someone who is well acquainted with most of the route living now in Oregon near Eugene and having lived in San Luis Obispo County for 20 years with parents who live in Ventura County, I would take all 3 days. I’ll share what I would do with the following assumptions: One, the car is in good shape; and two, there’s a lot along this route you haven’t already seen.
The whole PCH is fabulous, but some parts are more fabulous than others. As much as I love the stretch between Morro Bay and Monterey, I would avoid this route at this time of year. First, it’s filled with tourists, too many of whom are dancing their elephant-like RVs on a road not designed for them. Second, when The Valley is hot, it sucks the fog right in against the coastline. You could spend the entire miserable route following a Winnebago and looking out at nothing but cloud cover. Third, the route is much more spectacular traveling north to south. So as stunning as it is, skip it going south to north.
Likewise, skip I-5, unless you want to fill your days with the stench of slaughterhouses, dust and Sacramento. Eeeww.
Get an early start and take the 101 north to San Francisco. Push on a little further and spend the night in a funky little B&B in the wine country, in either Napa or Sonoma County. If you cut over to Guerneville at Santa Rosa, you’ll find a bunch of charming little places. This is a nice “compromise” route. Lots to see and do along the way, picturesque but not the torturous drive along the slow, curvy coastal route on the 1. You’ll cross the Golden Gate Bridge in late afternoon and if you time it right, you can grab dinner at any of a generous number of fine establishments in the wine country. Driving time will be about 8 1/2 hours, not including stops at charming farm stands, pictures snapped in Sausalito, etc.
Next day, maybe do a couple little tastings, have a nice brunch and then resume your route along the 101 north to Eureka. From Eureka, continue along the coast into Brookings, OR. THAT… is some spectacular country to drive, not to be missed. It will take you through some of the most gorgeous redwood forests you’ve ever seen. If you’re lucky, you’ll catch a herd of elk browsing in someone’s yard. No shortage of spots to take jaw-dropping photographs. Brookings is a sleepy little town with some stunning beach views. Again, I would pick a B&B in Brookings over a regular hotel. Lots of restaurant choices… you can’t go wrong with our seafood, but the vistas are the reason to be there. Be sure to try some of our boutique brews, if you’re into that sort of thing.
Day three, push on along the coast from Brookings to Newport. It’s beautiful the whole drive but it ain’t Big Sur – which is a good thing! Far less traffic, not as many twists and turns and just as gorgeous. From Newport, drive east on the 20 to I-5 and shoot up through the trees into Seattle. This is your longest day of driving, about 9 1/2 hours. But the scenery makes it worth it. Newport is a sweet little town, nice stop for lunch. Have halibut in one form or another if possible, try a few Oregon wines. We’re good at Pinot Grigio and Pinot Noir.
Anyway, that’s what I’d do. Whatever route you choose, take some time to enjoy it! So much to see and do all along the way between those two points!