When using Free Transform in Photoshop CS6, Photoshop will use the best resampling method for you. The method choice will be based on the transformation you make.
For example, if you make the image smaller, Photoshop will use Bicubic Sharper. If you make the image bigger, if you scale it up, Photoshop will use Bicubic Smoother.
However, if you decide you want to use a different Interpolation method from the one Photoshop uses when you are transforming the image, you can do it through the Options bar using the drop-down menu.
Enjoy transforming! 🙂