Most Americans (myself included) grew up with Hellmann's mayo, a nostalgic and familiar flavour linked with American culture.
Hellmann's is the mayo many Americans prefer. It gives tuna salad a typical background flavour and smooth, creamy texture.
Hellmann's balances tuna's fishy qualities. Since tuna is fatty and has an intense flavour and scent, Hellmann's mayo works well.
It's the salad standard. It's not too thick or heavy to overpower the sandwich's flavour. Mayo, tuna, celery, and bread blend well.
Southerners have long guarded this spice. Its acidic, rich, creamy tastes explain why. Apple cider vinegar adds bite.
Duke's tangy flavour cuts through tuna's nasty and metallic taste, a chef noted. It gives tuna salad a more sophisticated mayo flavour.
Perfect backup singer. It adds smoothness and richness and lets tuna shine. Duke's mayo isn't overly sour, so tuna is still the star.
The sharpness of the cider vinegar enhances the overall flavour, but it doesn't overpower the meaty notes of the tuna.