East of the Rockies, at least, we use SYP for our 2x dimensional lumber.
Douglas fir is rare over here, and sold as a 'premium' product.
SYP is a very strong wood, but it's probably not easy to get out west because it comes from the southeast, with Georgia and Alabama being the largest producers, but especially Georgia.
This all comes from being a carpenter for many years.
Douglas fir is also not a fir, for the record, and should not be viewed as a substitute for fir in just about anything. If I remember, I think it is a species of pine.