Top 3:
1. Dead Superman (or maybe they did him a favor?)
2. Mullet Superman
3. Keith Giffen Superman (DC Comics Presents featuring the Creeper)
For me one of the worst version was the whole 'Death of Superman' comic in the mid-90's. Just did not like it at all. Thought it was just a strange publicity stunt. That and I didn't really care for the animated series either.