I think out of all the Big 4, Anthrax had the most punk rock spirit. I also think that this is why they transferred to hip hop so easily, a lot of the same attitudes from punk rock were found in early hip hop. Not soulless, but a different type of soul than what you'd find with Metallica or Slayer. Also, I liked Anthrax a lot because their vocals are so melodic. Belladonna often sounded like he should be singing in a 70's hard rock band, not a thrash metal band. It created a nice balance.
Bush period mostly sucks though.