To elaborate and expand on my top four, I decided to categorize my all-time ranking of Universal attractions. Note that to qualify for this list, it must be an attraction (and not a restaurant or store) that is either currently in operation during day hours or at some point operated for at least 365 days (therefore excluding HHN stuff, because that would make things very very very messy) at either Universal Studios Florida, Islands of Adventure or Volcano Bay.
My top 8 are super easy. Lack of gaps represent hair's width differences:
#1--Dueling Dragons (pre-Potter)
#2--Men in Black: Alien Attack
#3--Amazing Adventures of Spider-Man
#4--Harry Potter and the Forbidden Journey (only this low because of the plot, or lack thereof)
#5--Jaws
#6--Hagrid's Magical Creatures Motorbike Adventure
#7--Back to the Future: The Ride
#8--Universal Horror Makeup Show
After that, there's 11 attractions that I can't pick just two of, heck I have no idea how I would order them. They are, in no particular order (besides counter-clockwise through each park): T2 (at least in its time, was very dated when it closed), ET, Hogwarts Express (my representative of Diagon as a whole, without factoring in the mediocre Gringotts), Disaster, Mummy, One Fish Two Fish (yes really--my representative of Seuss as a whole), Poseidon, River Adventure, Popeye, Te'awa and Kala/Tai Nui.