Giant canyon swing always gets me. Obvi it has the positives and floater like any s&s swing, but the acrophobia of feeling like youre about to be hurled off a cliff, combined with the amazing scenery makes it such a top notch installation for me.
Seconding Zippers, such an old school and intense experience. Speaking of old school, I got to ride a Roll o Plane for the first time recently at Knoebels and that was super fun too, and surprisingly intense.
I think Screaming Swings in general would be my 2nd favorite. I'm just always annoyed by how short the ride cycles are!