If we are talking about condiments to put on hot dogs or pizza, I'd pick ketchup over mayo but the thing is, I never put those topping on my snacks unless they are subpar and I want to make them palatable. Mayo doesn't taste good by itself and ketchup just make anything ketchup flavored.

I'd go with mayo over ketchup because there is some dishes like potato salad which require mayo but I don't know of a single dish which has ketchup has a necessary ingredient.

Oh, and for those confused why I'm making a Splatoon strip so late, Nintendo announced they are doing an extra Splatfest about those 2 choices next month.