well neither place is just ONE theme park.
universal orlando is made up of 2 theme parks (universal studios and universal islands of adventure) and partnered with 1 water park (wet n wild). plus there is city walk which is a place with shops, restaurants, clubs, and a movie theater. they also have onsite hotels.
and disney world is made of 4 theme parks (magic kingdom, epcot, hollywood studios, animal kingdom) and 2 water parks (blizzard beach, typhoon lagoon). plus there is downtown disney which is a place to walk around with shops, restaurants and other entertainment including a movie theater, cirque du soleil show, and disney quest which is a huge indoor arcade. disney also has a sports complex, golf course, 24 hotels,, and other activities throughout the property.
there is no way to get either place done in ONE day.
out of the parks in universal orlando i would recommend universal studios.
out of the parks in disney world i would recommend magic kingdom.
now picking from those 2 parks i would definitely choose magic kingdom over universal studios any day. so i would recommend you go to magic kingdom with your one day in orlando.