Exactly, calling Ryan a dark horse is laughable.
Seems like he has a huge young female-based following, and from talk on here, it has been implied that he has a lot of strong cashed up support.
He's the most obvious choice... it would be incredibly boring if he won. He actually would be the most forgettable winner in Big Brother history. Right now the only person I see as a possible dark horse who could win is Priya. She has never been the most popular, most saved, most likely to win, etc. But she's unexpectedly come a long way, when people thought she would be a goner the week Dion/Katie left.
David is your 'underdog' character who a lot want to win. Skye is the princess who most younger viewers like. Travis is... well, yea popular for some reason.