When will you be there and for how long? What are the kids interests?
Someone just asked this on the Universal forum, and in their situation I said SW, but with only the info you provided, I’m leaning toward Universal, especially with your kids ages.
SW is good if you have only one or two days, aren’t into thrill rides, have young children who wouldn’t meet height requirements for rides at most parks, and enjoy aquariums / zoos and educational themed attractions. The Fun card is also a good value if you are local or plan to return on future trips or plan to visit for different holidays, especially Christmas. However, I know we’d get bored going back day after day on the same trip. Two days here and we are ready to leave.
Universal is better if you have 3 or more days, love thrill rides, can meet height requirements, and prefer movie based attractions. It tends to be geared more toward teens and adults. The season pass is a good deal, but it’s important to note it does have black out dates, including the entire month of July.
If I’m going to be visiting a place over and over again in the same trip, I’d choose Universal. With two parks verses one and Citywalk to explore, there’s much more to keep you entertained. I’ve done week stays at Universal before, and while it was more time than we needed to see everything, we never got bored and couldn’t wait to plan our next trip back.