1 day is PLENTY for Universal Hollywood. It's a very small park, much smaller than Orlando. There are only 12 rides, 1 studio tour and 2 shows. If you're going on a quieter time of the year and on a weekday, you'll get all that done in a day. If you're going on a busier time or the weekend, get the VIP - so worth it.
The number of days at Disney depends on how you Disney. <--- used Disney as both a noun and a verb! Yay, me!
If you're with a slow group of grandparents and small kids, 5 days isn't enough. If you're 2 able-bodied people who go from rope-drop to closing, 3 days is perfect.
The last time we went to
Disneyland, we were in a group of 10 people. 3 grandparents, 4 parents, 3 kids. We were as slow as molasses. Arrive to park an hour late, oh, need to rent wheelchair things, get inside. People need to use the bathrooms. Finally get to a ride - some grandparent has wandered off. Gotta find them. Ride one ride. Oh, now more bathroom breaks. Oh, someone is tired already - needs to go back to the hotel. Okay, it's almost lunch time anyways, let's go back to the hotel.... and so on.... we got maybe 5 rides in each day. 5 days weren't enough.