MGM vs Universal

In a short while I will be headed off to the lovely land of Disney World. I am totally stoked about a vacation, a well needed break away from here. As my family and I plan the trip we are trying to work some things out. We thoroughly enjoy MGM, the great rides and entertainment. We have never been to Universal Studios and are considering going there, I'm wondering is it fun? Do you think you could spend more than one day there? What are the best things to do there?

What is your favorite thing to do while in Disney World (restaurants, activities, events...)? I am open for suggestions, so if you have any I would love to hear them.