I'm sure you'll have a great time whatever you do. I delegate Orlando trip planning to my 19 year old who is in college. // Not sure if you want to pick parks or let your son pick. If you've always wanted to do Universal for a few days why not. There are always other chances to come back to WDW, and anything in Orlando is a pretty good time. I've been letting my son do the planning since he was 7, subject to my budget and approval. // I like them all, don't care where we go, and am more into having fun with family than anything else, so anything works.
For my son who is 19, Universal is more of a day park. He likes to do a day if they have new HP stuff to see it, but doesn't care to hit it every trip (Almost always gives it a skip, but has allocated a day on our next trip to see Diagon Alley, Gringotts, and the train). He thinks all the parks in Orlando including IOA and Island of Adventures are world class and worth doing, but his preferences are (1) SeaWorld (2) Disney with the Magic Kingdom being his favorite, but liking all four // Hollywood studios next, then Animal Kingdom, and then Epcot (but all good) and (3) Universal (He can cover everything he wants to do with a one day park to park pass.). He likes Discovery Cove too, but thinks it's overpriced, and almost always has us skip that one because it kind blows the budget that I give him, and he'd rather do a longer trip. lol He by the way really likes Cedar Point in Sandusky, OH with its' 18 coasters too and puts that behind SeaWorld and the MK, but before the other Disney parks in his park preference rankings, tends to go for favorites the most, but does mix things up a little.
Most on this forum, though, like spending more time at the Universal parks than we do, and many advocate three days. Most think onsite there is a real treat. I'm a die hard budget trip offsite visitor who does a little mini trip to the area annually, and just think doing Orlando period is a treat.
I'd personally do WDW and just hit Universal for a day, but that's just based on what my family likes best. And you are talking big dollars doing a few parks vs. just Universal, so look at the budget too. Multiple days at Universal is pretty cheap, but we never want to do more than one day there.