What do you do with it?
The 11" is a beautiful little machine, I would personally avoid the 13" Macbook Pro, as the 11" screen resolution is a great deal sharper. If you need more real-estate, then I'd recommend using an external monitor when you don't need to be mobile.
If you had the option, I'd go for the 13" 2011 Air. If you don't have the cash now, and you can wait, it's by far the best option, IMO.