I think mountains are more interesting and 100 % more scenic than the coast. If you've seen a big body of water, you've seen most of them. That said, US 97 is hot, brown, and barren in some places, and it's the most direct mountainous route. There isn't something like the PCT trail for bikes or cars.

The climbs depend obviously on your physical condition and on your route. But if you're sticking to paved roads, none of them are terribly steep. You won't find anything more than a 10 % grade on the main routes.