I say WDW, you will probably find much to do without the kids that you have never seen or noticed before.
In the off-peak times, I can get through both Universal parks in one day with time to spare. I can start at IOA in the morning, stop for lunch at citywalk, head to USF in the afternoon and then return to IOA for a last ride on Hulk or the Dragons in plenty of time, even with an off-peak 7pm closing time.
If you are spending 4 days, I am afraid you would be at a "that's it" moment with Universal sometime in Day 2. We always do 1 day at Universal and get our fill, and then 5 at Disney wishing we had more time.
Nothing against Universal, I always have a blast there. But if you are a WDW nut, you are best to spend your time there.
But that's just me!