You should avoid including script tags in the head because it introduces single points of failure in your app. Losing a few ms of 'analytics' time is better than providing your users with a broken site because your analytics scripts (or any other hosted JS files) didn't load and waited 5-15s to timeout (depends on browser).

Steve Souders gives a great talk on this: http://www.stevesouders.com/blog/2010/06/01/frontend-spof/