Burger King's fries + onion ring sauce are amazing, what the hell is wrong with all of you?
Also, waffle fries can go fuck off. Trying to dip them into a typical ketchup cup is like sticking a square peg into a round hole.
Honestly all fries should be curly fries, because they are perfectly shaped to be dipped into ketchup cups and they condense the maximum fry flavor into the smallest possible area.
If you throw potato wedges into the mix, then KFC's potato wedges are the ultimate fast food side item. However, I would consider them slightly different than fries.