Aaah! I try to avoid sauces whenever possible to reduce caloric intake, particularly when I’m already blowing it on fries. What I love about sweet potato fries is that, while not exactly a healthful preparation method, they are more nutritious than white potatoes and they offer a wonderful sweet but salty complexity that russet fries do not. I think they taste just fine with just a little salt on them, preferable a large crystal salt such as sea salt. Ketchup destroys the sweet/salty balance with its acidity, so I can see going for a mayo-based dip, though.
levdrakon, I hear you. “Yams” with brown sugar (I don’t like marshmallows, though) are yummy for Thanksgiving, but mostly all that sweetness overpowers the sweet potato. A little butter and salt are all you need really. Come visit the South and don’t forget to order some sweet potato fries.