This is confusing to me. Are you talking about the religion of Islam or the current culture of Islamic regions? It really does alter my vote. If you are asking which religion is the most oppressive then the answer is Judaism hands down, no contest. If you are asking which culture is the most brutal and oppressive then I would have to say Islam. However if you change the region of the world then I might pick another religion. If we are judging the religion itself then the winner is clearly Judaism. I doubt anybody would be capable of arguing that.
Every religion has an equal opportunity potential of being taken far too literally and seriously by its vulnerable adherents so disposed, and within every religion a hierarchy festers that is eager to aggrandize itself through those that are vulnerable. It's just humans being human, and the gods couldn't care less.