Google analytics is amazing imo, the amount of detail it seems to collect is incredible!
I have found some very interesting things out with it.
Some of the most useful features imo include the page overlay so you can actually see which links are clicked most on a page, the goals feature which will help keep track of specific things you can set and the in depth links in/out information,
Ii must confess i have only used a free limited statcounter, and a long time ago, but never got on with it
