That solely depends on your purpose. If you are using a lot of OpenCL accelerated software then AMD 7000 series is the only way to go.
But if it is only gaming, I would propose a GTX 670/770 depending on what you can find around the 400 mark. The price is very dependent on vendor and country. You can do a further research on your own. This cards fall between the HD 7950 and 7970, but even if a 7950 is a better performance/price option, the lower temps and noise on the nVidia is something I would appreciate.