Paid tools are essential when you need advanced features, increased limits, historical features, or online support.
Sometimes, in order the wanted aim a free tool does the trick.
A/B Testing; Visual Website Optimizer allows you to run A/B tests.
The most popular of all the analytics tools available, Google Analytics continually innovates and sets the standard.
The Google Analytics API is great for building custom reports and tools, and also for pulling data straight into Excel or Google Docs.