There are plenty of camera review sites where you can find out so much about the camera and quality, these are usually a little bias towards Nikon/canon as these are the big players.
A quick Google came up with this...
http://snapsort.com/compare/Nikon-D600-vs-Sony-SLT-A58
Personally you need to make sure the camera has the features that you actually require, which I expect both of these do. The next thing I would tell you other than just buying based on image quality (These are both technically very good cameras and unless you are going for large prints will not notice a huge difference in image quality as they will massively depend on which lens you use) you need to go and handle the camera before making a choice. The button layout on the cameras is really important and some are just plain annoying with having to dive into menus all the time to access features you use on a regular basis.
Some cameras are heavy so lighter so you really need to handle the camera before coming to any decisions on what to buy.
Hope that helps/