If you're talkin' fast food fries, I'd have to go with Burger King. For regular french fries they're the best in my opinion. The next best would be Chick-fil-a with their waffle fries. And for curly fries, nobody beats Arby's. Some people try to say that Hardees/Carls Jr have the best curly fries, but they're idiots. If you've tasted both you would know that Arby's are vastly superior. You can find some Hardees' that do chili cheese fries (you know, the really sloppy ones you have to eat with a fork) and those are really good, something Arby's doesn't offer.
The best french fries I've ever tasted are from this local barbecue restaurant. They do like ribs and pulled pork, you know, that good old southern barbecue. Their french fries are insanely good. They have some sort of special seasoning that they use to give them the most unique flavor, kinda salty, kinda sweet. I think they put a bit of brown sugar in that stuff, it seems like I get a hint of that in the aftertaste. I'm pretty sure they fry them in lard too, no vegetable oil for those babies.