I like ketchup, but not on eggs or, as my cousins in my youth horrified me by eating, on macaroni and cheese. (Even worse, the macaroni and cheese--Kraft--was leftover that had been refrigerated overnight and then fried in butter. In case you should wonder, this does very little good for a food that is really not that good to begin with, and I say this as a woman who still loves that cheesy salty neon saucy delicousness).
Ketchup is for various permutations of meat and potatoes, often mixed with mayo and mustard (or sometimes ranch) to dip fries and fishsticks in (add relish and it substitutes for tartar sauce), slathered on crispy hashbrowns or corned beef hash, squirted on hotdogs, hamburgers, meatloaf, and that ilk.
I mostly use Best Foods (Hellman's east of the Rockies!) for all mayonnaise-type dressing applications (including potato salad, which does also include yellow mustard--just made a batch today, and it's delicious, if I do say so myself) but I retain a secret love of Miracle Whip from childhood when, I kid you not, I used to sneak into my dad's kitchen at night and eat it out of the jar. With a spoon.