I'm sick of Rage, but my runner up would be SSJ2. As much as I like it and the moments that accompany the form, you could replace the form Gohan uses against Perfect Cell with a juiced up regular SSJ and the DB series would barely change.
@Saapiniapple Exactly what I'm saying about SSJ2, it's not much different from 1.
You could even argue it would be a better writing choice for a juiced up regular SSJ to defeat Cell since they just trace back to mastering one form instead of getting new ones (the Grades).