Today I checked at my stats in Google Analytics, and also at Awstats.
The results are different, while the trend may be the same, well look at the numbers.
As you can see the number of visits to the site is 60,146, this is not unique visitors, these are total human visitors, (bots are supposed not counted), also there were 86,906 page views according to Google.
Now lets see AwStats.
Second column are the number of visits 82,472 and 155,478 page views (third column) according to AwStats.
Google report a 27% less that AwStats in visits, and why? that was my answer and after looking around for an answer I finally found that the difference is the NoScript add-on for Firefox.
And according to Analytics and AwStats Firefox is the most used browser to explore my site.
Lets see at AwStats
And now at Google Analytics
As you can see 70% of the visitors use Firefox, and according to this site NoScript is one of the most popular add-ons.
Google Analytics works because you install a java script in your site to count visits, if your visitor comes with Firefox with noscript installed that visit is not counted, and therefore Google Analytics will not report it.
But the most important thing about stats are not the absolute numbers but the trend they have, having statistics in mind it is supposed that the trend should be the same in both tools.
Also they have a lot of useful tools so it is recommended to use both of them.