get the 570 please, but if you can save some more money and maybe wait for a few weeks, buy the 580. or which I did was. I sold my 570 and got two 470's in sli, so much better performance all round. buy a pair of 460's they will cost you less than a 570, and if your system can support it, with those you will get a much better performance. You can go to anandtech.com and check out below a couple of comparisons:
AnandTech - Bench - GPU11 AnandTech - Bench - GPU11
However, if you must pick between 560ti or 570, then 570 anyday, yes there are some 560's that are crazily clocked that may come close to a 570 in performance, but they are also super expensive. and for few bucks more, you get an amazing card!