Someone can correct me if Im wrong but touring in the US is best going West to East and North to South.
Another thing, going down the coast would be better going North to South for another reason: you ride in the lane nearest the ocean. In some spots there are some nast edges if you were to ride South to North. And yes, there is a bit much traffic on the coast in the summer time. Mostly tourists in cars, SUVs, and motorhomes. But its a great trip.... going from North to South!