This is hard, but I voted USF. To break it down into a pros/cons list:
USF:
Pros:
More rides and attractions
Also has Islands of Adventure next door
Feels more like a theme park/has better theming
Close to Disney and SeaWorld which makes it easier to go to all the area theme parks
Has (mostly) the better version of the rides and attractions (ex. The Mummy, Hogsmeade as a whole)
Cons:
It lost a lot of the "we make movies here" vibe, and nothing is filmed there any more
USH:
Pros:
The studio tour itself is worth a ticket, it's really such a cool attractions/tour
You can tell it's a real, working studio
It's smaller and easier to navigator, minus the escalators
The views of the valley are really cool
Close to Hollywood and other studios (like Warner Bros) if you want a big "Hollywood" type vacation
It's the OG park, and that's worth bonus points
Cons:
Because you can see the backlots, office buildings, and valley, you do lose that magical "we're in another place" theme park vibe
Lesser attractions
Far from
Disneyland and Knotts, which makes it hard to have a theme park heavy vacation
From the two times I've been, I've felt like there has always been longer lines than at USF. I think because there are less "E Ticket" attractions so you have a lot of people funneled into not a lot of queues.
Escalators
As a note, I've been to USF a bunch before I went to USH for the first time. I was at first disappointed to see so many duplicate rides, but if you went to USH first you would be delighted to see all the new things to do. Perspective is probably a big part of your opinion of it.