Tough choice. I voted McDonald's but Checkers is up there.
I like Taco Bell nacho fries but I only get them as a Nacho Fries Bel Grande, and I wouldn't compare and rank that against regular fries.
I don't mind Burger King fries all that much, and while I think McDonald's fries are better, I find BK fries to be more consistent. When McD's fries are good, they are really good; when they're over-cooked or over-salted or not salted at all though, they're bad. And McD's fries still aren't as good as they used to be before they switched recipes (what was it, they used to use beef tallow and then they stopped? Or they use it now and they didn't before? I don't remember).
Cookout's Cajun fries are pretty good.
I don't care for Wendy's fries though, but I do like dipping them in a frosty. I really wish they'd just have their potato wedges from breakfast as an all-day side item so I could get them over fries.