So I know several people heading to Disney soon, and I like to consider myself a connoisseur, if you will, of both parks. What's my experience? I've been to both of them several times at different stages of my life, from being single with my boyfriend (Dean, of course),
to being married and pregnant with a toddler,
to having a child and a toddler, etc.
I would make a general statement that the younger your kids are, the better Disney is compared to Universal. There are mostly kiddie rides that aren't scary with only a few roller coasters. Once they start getting older and braver, you need to head to Universal.
Now Universal has 2 parks - Islands of Adventure and Universal Studios. Islands is where you'll find Harry Potter-land, and there is the Hippogriff coaster that's a good intro for the scaredy-cats. Dragon Challenge (Blue and Red - Blue is the best and ride in the front row) is my favorite coaster right next door, and reportedly my 10-year-old niece threw up in her mouth and was quite dizzy after she rode it, but it was her favorite ride after that. The little kids love Seussland but there's not much for an older kid to do other than be wowed by the cuteness.
Marvel Comic-land has stuff for both, but it's LOUD and crowded, so take a Tylenol first. Old Comic Strip-land is my least favorite part - it has a couple of water rides but that's about it. And what kids today know Betty Boop, Dudley Do-Right, and Popeye? Jurassic Park has stuff aimed at younger kids (a big prehistoric playground for example) but they do have a good river ride with dinosaurs.
When you're tired of that just walk 10 minutes over to Universal Studios (not a 30-minute bus ride like park-hopping at Disney) where there are 2 great coasters for the >48-51" crowd (Rip Ride Rockit and The Mummy, which is way more than a coaster), but there are plenty of things for the chickens, I mean the <48-inchers. Men in Black is the hipper equivalent of Buzz Lightyear, where you shoot at aliens, and Disaster is the equivalent of Backlot Tour at Hollywood Studios in Disney, but way better. The Simpsons is fun and actually entertaining for the adults with all Homer's one-liners. The really little ones will like the playground with water features next to the ET ride, which sucks and I don't know why they haven't updated that one yet, but it's ok for kids.
Now I've briefly covered Universal, and for Disney, let me direct you to the expert, Tour Guide Mike. If you are going to Disney, you MUST check him out. He used to work there and now runs his own VIP tour business. For $21.95 he finds out ages, preferences, etc. for your group and customizes a plan for you. You find out the best days to do each park, the rides to avoid, best restaurants, etc. It's exhaustive and you can get lost in the website, but with his tips we didn't wait in a single line!
And one word on Disney's Fast Pass vs Universal's Express Plus. It's the difference between socialism and capitalism. At Disney, you can get a Fast Pass for no extra charge that tells you what time to come back to the ride so you can go to the front of the line. If it's a popular ride, you may be told to come back in 3 hours, and eventually there won't be any more issued. Now at Universal, if you stay on-property or pay extra (ranges from $25-$70 depending on the day), you get an Express Plus which means you can go to the front of the line at any time for any ride except Harry Potter, Rip Ride Rockit, or Pterydon Flyers. I'm a capitalist, myself.
Finally, don't forget to take a break from the parks for a day, or leave early to get some rest at the hotel. Otherwise, at the end of the day when you're ready to head out for dinner, you'll end up with this.
Which makes it harder to get fired up for this.