Wow, it seems like most people here are pro-ATI I was always told that Nvidia was actually better than ATI and now hmm...
Most people are biased, that does not necessarily mean that one is better than the other. It just means they tend to shout louder and make claims without providing reference links.
Clearly, your question has been answered though, with a budget of $210, there really is no better choice right now than a GTX 560 Ti. The 6950's and GTX 560 Ti 448 Cores are too expensive; and the GTX 560/6870 are cheaper, but significantly less powerful. Refer back to that performance chart and keep in mind that the GTX 560 Ti listed there is one at stock clocks, while most of the models that you are likely to purchase are going to be factory overclocked. Bump up the performance to 950 mhz, and you will running more in the range of a 6970 and GTX 570... for $210.
To illustrate the point, the Zotac AMP! comes factory clocked at 950 mhz: