Canon and Nikon really are a horse a piece. Each has their strengths and weaknesses, but they both have good SYSTEMS as a whole.
Sony could have the greatest sensors in the world, but they don't have lenses, they don't have flashes, and they don't have third party support. In the current market, I could never recommend that someone buy a Sony dslr, no matter how good the sensor tests in DXO.
Actually, those Sony Zeiss lenses are excellent, as well as expensive, and the many Minolta lenses are excellent as well. Sigma has been making compatible lenses, and Tamron just signed on.
While Sony is not ready for all the professionals, they are getting there amazingly fast, and their decision to keep the Minolta lens mount means plenty of low cost used lenses of high quality are available.
The main objection I have to Sony as a professional camera maker, is Sony itself, and my concern that they may decide to drop out of the high end full frame market. They are an electronics company, and I do not know just how dedicated they are to staying in the high end market.