KiCAD becomes better and better after the CERN commitment to support it. At FOSDEM 2015 there was interested talk about KiCAD. There were so many people wanting to be at this lecture that lot of them were standing as there was no free place to sit in the small room.
Today we got even better news: now KiCAD have differential pair track routing feature and trace length matching!
Here is the announcement video:
These features will shoot KiCAD directly in territory which was reserved for PADS, Altium etc high priced professional tools.
To the best of my knowledge none of the popular amateur tools like Eagle, Designspark etc. have these features available.