I've never used a pulverizer, so I don't know about the relative merits of the two. The box blade is excellent if you have to move much dirt or if you want to change the shape of your land. With the scarifiers you can loosen up the seed bed as deep as you'll need. If you don't mind looking like an amateur, you can chain a board to the bottom, drag it around, and flatten out the seed bed quickly.
I say, buy the box blade, and rent the pulverizer. If that's your main grading project, you'll get a lot more use out of the box blade.