While sony does make nikon sensors keep in mind that doesn't mean sony and nikon sensors are the same. Sony makes sensors for many other companies but they make them based on the other manufactures designs and specifications. You'll notice from reveiws and tests Nikon sensors will usually score higher than Sony.
http://www.dxomark.com/index.php/Cam...Sensor-Ratings
In addition a sensor makes little difference between comparable cameras, it's the lens and the software within that really make the image.
For DSLR I would go either Nikon or Canon, your lens quality, selection, new and used availability will be far superior over other brands.