CDN-Please help

Hello,
I’m trying to install wp total cache plugin and it keeps telling me to enable my CDN. I’ve had a look around and found out that I do need and want this for my site as it will obviously be beneficial. But again as always there a million options.
Does anyone know which is best and most compatable with hostgator? Which is the cheapest and best value?
Also do I need to pay for it as I’ve also read you can get free plugin CDN tool, which does the same thing???
Thanks as always.