I have used a free tracker from Extreme Tracking before and found that to be acceptable:
However, their terms of service require you to place their icon somewhere on your page. In addition, based on discussions I have seen in other forums, it is not the best tracker (although, since I am just a hobbyist webmaster, it was good enough for my purposes.)
I later decided I didn't want their icon on my website, so I switched to Google Analytics:
https://www.google.com/analytics/home/
Google Analytics is the best free tracker I am aware of, providing way more information than most people will ever use.
I have also heard good things about StatCounter, but I have no personal experience with it:
I think the best counter is one that is server-based, and most web hosting companies offer such a service with their hosting. Does the host of your website not offer a traffic tracking service?