French fries are meant to be dipped. If they have shit dumped all over them, they are no longer fries, they are potato nachos. Which is delicious, but it's not French fries.
I sort of consider dipping fries and fries with stuff on them to be two different but related species of meal, pretty much exactly like the difference between chips-and-salsa and nachos. Frychos.
As to preferences, for dipping, spicy ketchup (mix tomato ketchup 1-for-1 with siriacha or other hot sauce); for frychos, fucking everything! Load em up: guacamole, chilli, cheese, onions, peppers, bacon, mushrooms, gravy, salsa, mustard, marshmallows, spinkles, alright alright I'm getting carried away now, you get the idea!
In the UK most fish and chips shop vinegar isn't malt but tastes just like it (most people don't even know). You can buy the same stuff online or get it from wholesalers.
I love disco fries & poutine, but its not an everyday thing for me. (Disco fries are like an American version of poutine with beef gravy & yellow American cheese instead of cheese curds)
I make a dipping sauce from ketchup & mayo and will variously embellish it with things like mustard/dill relish/sriracha or worcestershire/garlic/oregano/lemon juice
I also make a "buffalo ranch seasoning" with cayenne, garlic, vinegar powder and powdered ranch dressing.
Cheese & bacon bits with sour cream is another favorite.
Depends on the chips/fries and what the sauce is. Sometimes I want just a wee bit to add a kick, other times I want to be face pounded by some cheesy garlic goodness