If you have the time, riding the entire Pacific Coast would be great. Each state is a bit different. Washington has lots of trees and tree farms, cranberry bogs, Indian Casinos, and such. Oregon also has lots of trees but it also has dramatic coastlines (and a couple tunnels) and the route keeps the coast in sight. California has lots more people and cars but, in my view, the Northern California coast is the best of all. The
ACA Pacific Coast Route actually starts in Vancouver BC, which is worth a couple days exploring before starting the trip.
If you are only doing 500 miles or so, my suggestion would be Fort Bragg in Northern California down to San Luis Obispo. This ride, done almost entirely on the California Coast is visually stunning. While the Redwoods in Southern Oregon and Northern California are definitely worth seeing, south of the Redwoods you have to ride on the shoulder of 101, a fast freeway that undulates through uninspiring scenery. The route hits the coast north of Fort Bragg, which is the big town in this part of the world. Maybe you can combine a bus/car trip to see the Redwoods and then drive down to Fort Bragg and start your ride from there.
I've done a ride from Bellingham, north of Seattle down to near Portland. It was an OK ride. You can read all about it and see many photos in
my journal of that trip.
I've also done a short tour from Fort Bragg down to Petaluma. It was only 3 days of riding but it is magical. You can read all about it and see many photos in
my journal of that trip.
I've ridden from SF (where I live) down to LA (where I grew up) many times. It is a fabulous ride, as well. I wrote
a guide about the ride from SF to LA, which will give you some idea of that ride and its planning challenges. I've written 2 journals of rides I did from SF to LA. You can read them here:
SF to LA journal 1 and
SF to LA journal 2.
No matter what you choose to do, it is hard to make a bad choice on the West Coast!