Eric Enge and his team at Stone Temple Consulting have done an excellent job on researching the various benefits of the major analytics providers. As a person who uses many of these tools every day, I can say this is the best resource I have ever seen. You can bet that any client I have that is looking for analytics will be given a copy of this report.
The report is academic in nature, but definitely not a snoozer if you are into Web Analytics, and I am. Take a look.