Nothing really to complex about why sweet potatoes are better than white potatoes but here is a little break down
White potatoes are mostly complex carbs.
White potatoes aren't as calorie dense as sweet potatoes.
White potatoes don't contain as much fiber as sweet potatoes.
White potatoes don't contain as many vitamins/minerals as sweet potatoes.
White potatoes have a higher GI rating than sweet potatoes.
White potatoes aren't necessarily bad, I used to eat one a day while I was on my last cutting diet and I managed to stay around 7-8% body fat. Just now when I'm cutting or maintaining I'll eat sweet potatoes over white potatoes though b/c of the added benefits to it.