Why rank empirical legal studies so high? Legal scholarship has [choose one or more: hidden from/ignored/avoided/succeded in downgrading] empirical studies and has paid the price in terms of its status within the academy in general. It is true that the vast majority of legal scholars (a) are not trained to perform empirical studies and (b) do not desire to excel at empirical studies. But in no other discipline of social studies would any serious scholar suggest that empirical work is anything but the most important. Theory is important too, of course, but the bottom line is that theory without data is just theory, and data without theory are just data. You really have to have both in order to advance the ball, and in the end it is the empirical work that tests, refines, and validates the theoretical work. For more see the Empirical Legal Studies blog and the Journal of Empirical Legal Studies (the logo of which appears above). Also, a disclaimer: Although I hold a social sciences Ph.D. and have been trained in and conducted empirical studies, I don't like doing it and am not that hot at it, so my placing empirical legal studies at the "top" is by no means playing to my strength.
Impact should be the primary quality criterion. I agree. The problem is that impact is often not measurable until years after the work is published. Moreover, my typology was in part a suggestion of what kind of scholarship in general is likely to have the most impact (though I recognize that any type can have significant impact).
What about legal history? I did not include legal history as a separate type of scholarship because, as I see it, legal history methods contribute to each of the types of scholarship I described. In other words, legal history can be used to trace doctrine, to examine underlying normative trends, to illuminate legal theory, and to examine empirical trends.
What about casebooks? My typology covers only sholarship appearing in journal article form. Casebooks are important sholarly contributions and can have tremendous impact, but they are a fundamentally different form of work. Most other disciplines differentiate between articles and textbooks as well.
Why rank at all? My list would have been far less controversial had I simply called it a typology and jumbled the order. But I believe it is important to have a discussion about what kind of scholarship is more likely to contribute to and advance understanding of law and legal systems.
So, I stick by my list, though I have appreciated the many alternatives and refinements that have been suggested.