Alright, I found my copy of Eating on the Wild Side.
There’s a whole chapter on potatoes (sweet potatoes are a different, species), but if you get one thing out of it, it should be “Choose the most colorful potatoes – blue, purple and red are better than yellow”. And eat the skins.
What the entire book is phytonutrients, and here is a specific measurement for potatoes ( I am estimating the numbers from this graph )
Measured phenolics, mg/100g (more is better)
Purple Peruvian ~ 200
French Fingerling ~ 60
Large Purple ~ 50
Ozette Fingerling ~ 50
Ruby Red Crescent ~ 20
Russet ~ 10
Yukon Gold ~ 5
Kennebec ~ 1
Regarding sweet potatoes, she says they are better for you, higher in antioxidants and lower in glycemic index. And again, the red, purple and dark orange ones are better than lighter.