Frozen yogurt is actually made from milk curds they same way that yogurt is. Ice cream is made from the cream that is separated from milk when it is processed. The curds in yogurt are good for your digestion and better for your diet.
Well honestly, the difference is obvious. Ice cream is milk, cream, sugar, etc. But frozen yogurt is simply that, frozen yogurt. But if you're going for the healthier choice, frozen yogurt is the way to go.