Hi,
It really depends what matters to you about accomodation - for proximity to accademic buildings (apart from History), Cripps and Hugh Stewart are best. For proximity to sports facilities, Nightingale is only a 30 second walk across the grass. For a community atmosphere I have heard that Florence Boot is very good, as it is a relatively small hall, and everything is in one (beautiful) building so you get to know people very quickly. For high spec. facilities I believe Nightingale is the newest - with larger room sizes and the majority being en-suite.
I stayed in Sherwood for 5 days on a conference, and I found the bathrooms to be dark, cramped and stained, and the walls paper-thin, but it all depends on what you want out of a hall.