Sweet potato or yam — which is better?

My sons are coming for dinner, but I hope to give them something much more valuable and enduring than a meal and some gifts. Something I was never given, so today I’ll be giving it to myself as well. Finally, I will determine the difference between sweet potatoes and yams. Two different recipes — one sweet, one savory –each made twice, once with yams, once with sweet potatoes. May the best tuber win!