Well, Apple of course.
I probably spend too much time thinking and analyzing Apple, Inc. While most would label me an ifanboy, and rightfully, so, I think I'm cognizant of the market they play in as a whole, and recognize good things from other places.
That being said, I think 2013 will prove to be a very interesting year. Tim Cook let the company run "as Steve left it" for a year. A wise move. Now he has reshaped the executive list to better fit his style and way of thinking. It will be interesting to see how this team releases products and what types of updates they think are important.
Apple will get new pressure this year from the mass of Android devices. Also, MS is making a huge push with Surface and Windows Phone 8. If Apple maintains it's lead in revenue in its ecosystems then they'll be fine. If it slips with MS and Google devices gain market share and revenue share, then Apple will find itself on the ropes again in short order.
Personally, I think they'll be fine. However, it will be an interesting year.