A true optimist would say Italy, but as long as they finish above Scotland, I'll be happy! (I have my reasons).... plus, you've always gotta love the underdog! As always, it's got to be between: England, France, Ireland and Wales.
IMO though, Ireland don't have what it takes this year to compete and France is as always an unpredictable entity. It's got to be between Wales and England for me... and of course I'm going to say my money is on England.
Why? Because I think that the progress can be seen with the team growing as a unit. First game of England vs Wales will almost certainly put to bed the question of who will dominate this year's six nations!