We used to be Disney obsessed and went as often as we possibly could. Now, after our first visit in January, we're huge Universal fans. Here are some of the reasons.
1. If you like staying onsite, the Universal hotels are much better. Bigger rooms, attentive staff, and it still costs less. Your room key gives you a great perk; FRONT OF THE LINE ON ALMOST ALL OF THE ATTRACTIONS!!!!!!!!!! They really spoil you for spending the money to stay onsite. You show your room key at an attraction, and they show you a separate line with a very short wait time. Show your room key at a restaurant, and you get priority seating without reservations. If you're not staying onsite, you can still buy an Express Pass to get front of the line (FOTL) benefits once on each attraction.
2. Universal is less crowded than Disney.
3. Universal appeals to everyone from very young children to coaster junkies, and everyone in between. When we used to go to Disney, I always wished they'd think about putting more coasters in. Universal isn't flooded with them, but they have several spread throughout the park to give you that adrenaline rush periodically if you want it. And they also have plenty of fun things for little kids. Play areas with water for hot days, well themed rides, and shows that appeal to every age.
4. Our first visit, I was expecting the Universal theming to be a step down from Disney. I was pleasantly surprised! The art, design, concepts, detail, flow, etc. were just as good (sometimes better) in my opinion. It was really fun to explore all the different areas and see new things. Like Disney, they very effectively create completely different worlds for you to enjoy. Take a look at the Picture of the Day string.
5. Restaurants. Disney has more sit down restaurants in the parks, but you don't have to make reservations months in advance to eat at Universal restaurants. Especially if you stay onsite and get priority seating. And City Walk has a wide variety of sit down restaurants to eat at. The food is great! Even the quick counter service food that we tried (Louie's and Burger Diggs) was really good. And again, you didn't have to wait an hour in line for it. It's just easier to get really good meals at Universal.
Those are the things I can think of just off the top of my head. If I think of anything else, I'll let you know.

I hope you enjoy your first trip to Universal as much as we enjoyed ours! We can't wait to go back, and I'm trying to plan our next trip right now!
Tamie