GA needs Javascript. Browsers that can't execute Javascript and browsers that aren't allowed to execute Javascript will not execute that code. So GA does not get all information. How reliable can the output of GA be, given that lack of information? "Garbage in, garbage out".

Apart from that, I once invested some time to dig through parts of the GA Javascript code. I don't remember all details, but it seems that the code sends back a lot of information to Google, and not all of that information seemed to be related to web statistics. It seemed that Google used the GA code to compare what was sent to a real browser with what was send to Google bots.

AWStats is written in Perl. That's about all the positive facts I know about AWStats. When I used it last a few years ago, it made tons of wrong assumptions about sessions and users, and its only real use was to find broken links. But that could also be done with a combination of grep 404 error_log, sed or awk to find the page and referrer urls, and sort -u.

Alexander