Total newbie to Universal here- what’s the difference between the two parks?
We usually hop as well, especially when we have AP's.
IoA , as others have said, has the wet rides, and the IoA wet rides are VERY wet. In winter, they are sometimes closed. We often skip them, or do them as a group.
IoA has Hulk, Kong, Seussland, Hogsmeade, plus a few others.
US side has Diagon Alley (I'd say more detail than Hogsmeade), Minions, Mummy,Transformers, E.T., Simpsons, Men in Black, and the night time movie show at park close, plus a few others.
Of the two, we probably spend a little more time in the US side as well, but it is a bit of a toss up. I think the difference is some of the rides we repeat. We often go on Mummy and MIB twice in a row.
The new HP ride will be coming soon to Hogsmeade. They also have a little light show they do - or maybe sometimes do - on the castle. I'm not 100% on how often, except the area only hold a limited # of guests, so you have to arrive early to be admitted. It was fun to see, but we don't see either show every night. (They aren't quite as spectacular as WDW's night shows, IMO.) If new ride is a great, we'll maybe favor IoA.
I should add, at WDW hopping = lost park time between parks. At Universal hopping = an extra ride, AND more efficient park touring, especially if you buy one of the wands and stay onsite.
If you get a wand, stay onsite/go all-in...then you quickly realize it is a pain to carry the wand around all day/night. Wands often have to be stowed in a locker when going on rides. the lockers are free, but they take time, and well, wands are a bit awkward to carry.
So...it is much easier to only carry them part of the day, and hopping makes that easier.