Best fries excruciatingly hot: Wendy's
Best fries hot: McDonald's, old school style
Best fries getting lukewarm: Wendy's
Best fries cold: Burger King (if you have to)
Best fries that require a drink: Arby's curly fries
Best fry-sandwich combination: McDonald's, with Filet-o-fish. Try the fries with tartar sauce. Do it.
Best way to eat ketchup: with pepper and salt mixed in, Wendy's.
Edited to add: Best fries ever: MOM.