That’s where the problem comes in with Heirlooms. However - they’ve GOT to be tough as nails in order to have survived so long.
Puzzling! :)
As for Heirlooms, the best tomatoes I’ve grown with some disease resistance have been:
Cherokee Purple (LOVE!)
Brandywine
Amish Paste
Constoluto Genovese (LOVE!)
Mr. Stripey
Black Krim
Arkansas Traveler
I grew the Amish paste tomatoes.
However, for flavor and uniformity of fruit that is always unblemished, I go with the Heinz Sauce tomatoes that I have only found at Territorial Seed Co.