American Shorthair vs Russian Blue

The 'all-American working cat' story implies a hardy, mixed-heritage constitution, but this is a closed pedigree bred like any other purebred, and Cornell's feline health center lists American Shorthair among the breeds with an elevated rate of hypertrophic cardiomyopathy — the same silent heart disease people specifically worry about in Maine Coons.

Russian Blues are one of the few purebred cats without a well-documented breed-specific genetic disease, so the real caveat here is temperament rather than health: they are genuinely reserved with strangers and slow to adjust to change, and a chaotic, high-traffic household will stress this breed more than most.