Spider-Man hands down! Transformers is also awesome, but it's merely Spider-Man 2.0.
Of the "classic" rides, I'd say Jaws was the best.
I'll probably get crucified for this, but the most overrated ride in Universal's history: Forbidden Journey. Awesome queue, cool theme, innovative ride system, but the ride itself isn't that great IMO. It's even less desirable if you're not a Harry Potter fan and have no clue as to what the story is about. Have ridden it over 50 times, and it simply doesn't do it for me.