We're doing both parks in 2 weeks. I look forward to adding more input and a vote once I visit. My only apples to oranges comparison was way back ~1990 when I went to then named and recently opened MGM Studios, and Universal Studios FL in the same visit. I have not been back to either place since. I do remember at the time LOVING US FL, and MGM was only "OK" in comparison. To be fair MGM was still being developed and didn't have a lot.
My highlights from MGM were: Indiana Jones show, back stage lot tour thing. I honestly don't remember much else and I don't think there really was too many attractions then.
US FL had Jaws (broken haha), Kongfrontation, Earthquake, pyscho house prop, some movie makeup show, and a cool ghostbusters show, Beetlejuice character walking around, overall atmosphere was just BIG..... and other things that blew me away.
For this trip, which includes my 3 kids (6.5,7.5,9.5) I'm most looking forward to the following at each park (we chose IoA for the kids over US FL)
HS - MMRR, SDD, Indiana Jones show, Fantasmic! , Sci-Fi dine in
US IoA - Seuss Land, Hagrid's motorbike/HarryPotter area, Jurassic Park.
One minor disappointment is the weaker linup of shows at US IoA....I see Poseidon's Fury which looks cool (I'm not sure what this is exactly but I think its closest to a "show"). Seussland has something with the characters, and there is 1 or 2 small things in HP area....Other than that no parades and no major shows I can find. A little surprising. Still the places looks amazing from pictures and has a very strong lineup of actual rides.