Correct me if i'm wrong but wasn't 'Fifty shades of grey' released as an ebook, before the real publishers saw it's popularity and bought the rights?
I believe that was released as fan fiction and then an ebook. Yes then she got picked up.
Publishers have their eyes on self-publishers
Ultimately if you can pull in the numbers, they will come knocking
Though there are many self-publishers who are turning them down because they don't offer anything better than what they already have. Others are taking them up but stipulating very specific terms that allows them to keep self-publishing but allows the publisher to handle print versions
Which is the best way? It doesn't matter. Once you have a bestseller then you can worry about which way to go, until then no one is coming knocking and no one is going to treat you the same way as Stephen king, until a writer can demonstrate that they can pull in the big bucks.