I am choosing one of the following to test with: Telerik Free Testing Framework and Selenium
The web-project, is a site written in C # and JavaScript.
Can you please tell which of the testers to choose and why?
Highlighting the differences of the above tools for testing?
Full disclosure: I'm the Evangelist for Telerik's Test Studio and Testing Framework, so I've got some biases here.
WebDriver's awesome. I still do lots of workshops and talks around it. Telerik's Testing Framework (free, with a paid support option) has a great story around cross-browser compatibility, implicit and explicit waits, and a few other areas too. It's also a natural progression from that to the full commercial version of Test Studio -- however, you expressly do NOT have to go to the paid tooling if you don't want to.
Either tool will get the job done. The more important aspects of your long-term success with test automation are how you go about the work. Focus on using the Page Object Pattern well (regardless of which framework you use), and learn how to deal with synchronization around dynamic content (AJAX, e.g.). Get those two concepts nailed and you'll be a lot happier whether you're using WebDriver or Telerik's Testing Framework.