Federle was my favorite paste tomato for quite awhile; and like the other tomatoes I grow, I was saving my own seed. Unfortunately, it proved to be highly prone to crossing... after 2 generations, crossing was about 50%.

It might have made interesting breeding material, but I don't have space for that, so all of the seed was discarded. If I ever grow it again, I will bag blossoms for seed. San Marzano Redorta is very similar, and does not appear to cross easily.
I also grow Hungarian Heart, it is a tasty tomato & incredibly productive... but I wouldn't categorize it as a paste type. Amish Paste did not seem as flavorful to me as the other two.