I need to find the best route from Southern California to San Francisco to Seattle. I am traveling with my Mom for a medical appointment so we won't be getting out and doing many touristy type things. But I would like to find a guick route that is also pretty so that she can enjoy the drive.
Quickest is I-5
By far the quickest route is I-5. It's certainly not as pretty as the coastal highway, but it's a lot quicker...and I do mean a lot quicker. You really need several days to do the coast highway. Preferably at least 4 days. You can get from Seattle to Southern CA (LA area) in about 18 hours driving via I-5. It's been awhile since I've been on I-5 south of the San Francisco area so I don't remember what kind of scenic views it offers but I think the drive through Northern CA, Oregon, and Washington is very pretty as far as interstate highway driving goes.
101 is also a good option
While nothing is as fast as I-5, (except in Tule Fog season), you might wish to consider US-101 through the coastal mountains and valleys. For all intents and purposes it is interstate quality for 90% of the route. Speeds are comparable to I-5 and a Fall trip will be great.
North of Eureka, it slows somewhat going thru Redwood National Park, (oh what a shame!) and then if speed is beckoning, you can cut over to I-5 again on US-199 (joining I-5 at Grants Pass). If timing is still OK, US-101 continues north along the Oregon coast -- a little slower than the California section, but so beautiful!