there is no one specific place where you can both show off the work and link back to sell it, unless you make your own webpage. many places forbid outside links, though adding them to your bio or sigline is sometimes ok. i don't think there is one best though. i avoid flickr and deviant art, because it's too easy to accidentally give your large image away. and on flickr, i don't trust them with getty there. getty will take any image that is offered for free, and then put their own copyright on it. but any place that at least has your name is a good place. but every place takes time to build that up. and while your building that up, your not making new art.