I have a landing page I want to a/b test by either varying an element (e.g. button color) or serving two slightly different pages, and I want to track the performance of each. I've come across a wide range of services, such as paid tools (e.g. Optimizely), gems like Vanity, and Google Analytics Content Experiments, so I'm hoping to get recommendations on the easiest and least expensive methods for DIY a/b testing.
Also, if your recommendation doesn't have documentation or a tutorial, a simple explanation of the process for manually setting up and running an a/b test would be great.