For the same site how do two different web analytics tool report different data (unique visitors, pageviews etc.) The local log file analyzer (awstats) differs from the above two as well. Which one is more accurate and why the discrepancy?
Google analytics is probably the most accurate because they are giving you data off their own personal search engine versus a 3rd party stat counter. They may count unique visitors differently. For G analytics I believe it's every 30minutes if a person comes back it counts as a new visitors; on stat counter it might not have a set time. Other reporting tools also count bots and essentially fake visitors but in my experience Google analytics shows only real visitors, and very accurate down to the actual keyword people used since most of the traffic comes from their personal search engine - Google.
The differ because Google can count things that other stat counters cannot. As GameFriends.com said, Google is taking stats off of their own search engine. Therefore since it is theirs they will always be more accurate.
google is more accurate than any other stat shower. google uses information from their search engines so thats why they are more accurate.