I'm roasting potatoes in duck fat and want them to be awesome!
I would use yukon golds - baby ones or fingerlings
Honestly, I like russets for roasting because they get so creamy inside while the outside gets nice and crispy.
Russets. But any potato - red, white or other - tastes pretty good roasted with some olive oil, and pepper. Just don't overcook them.
I firmly believe in russets, wiped with olive oil, then a generous sprinkling of coarse sea salt, 400 F oven until you can put a knife in and out easily. Nice crispy skin. Works good for double baked too - scoop out the insides, mash up with some butter or sour cream or horseradish, stuff back in and re-heat. Also, you can save the skins for an appee (mash up the insides) and stuff the skins with your favorite filling.
If you're roasting in duck fat and want all that ducky fat infused in your potatoes, I would suggest russets (sliced)on the stove top or roasted in the oven (wedges)