Google Analytics is the best.Google Analytics is arguably the most popular analytics package available for individual site owners.
All most people are trust on google analytic it's all most accurate but yahoo analytic are also too good but it's paid tool. i have used it. i proffered yahoo analytic also.
I would recommend running multiple analytic applications/software for your sight (if you can afford it). I run google analytics and kissmetrics. its been working out well for me. But also, you can run analytics and not know what you are looking at. make sure you do your homework/research, know your goals and metrics to follow the most carefully.