I would go to Berkeley, the trioika of Pierson Hacker and Levy tops Harvard if you are set on a qualitative/historical approach.
Though if you are into welfare state politics (and aren't commited to a geographic focus) there is nobody better than Torben Iversen and Peter Hall at Harvard. Though, American, is relatively weak at Harvard.
In all honesty, you can't really go wrong with either so go wherever you think you would be happiest.