Potatoes are very low glycemic index* and have potassium, fiber, B6, and an alright amount of protein. I will fight for potatoes.
Edit: preparation matters, just mashed potatoes are super high glycemic index, but boiled waxy potatoes with the skins on alongside a protein is at the top edge of low or medium glycemic index. I will still fight for potatoes, but they probably need to be a side dish if you are looking out for your blood sugar.