I like Hitslinks because it show realtime data on your site stats and the interface is very easy to understand. But the problem is, it is not free and lacks other features for advance traffic analysis. Google Analytics is the best because it provides advance analysis tools and it's free but it is not real time.
Google analytics is not as accurate as it never matches my web host stats but it is still nice interface and most popular
google analytics is the best one you can opt for. if you have hosting, you may also have access to awstats, which is also a really cool one. I have recently seen people using sitemeter, you can give it a try too. Good Luck