The 6670 is the best card out of all of those you listed. The 5670 is slightly slower than the 6670. The 5570 is the slowest card, and I would only recommend that card only if you have a very, very weak power supply (something like 250 Watts) What resolution are you going to be playing at? If you are playing at a lower resolution like 1280x1024, the 6670 will perform well in most of these titles, though you will probably have to use reduced details on Battlefield 3 and Witcher 2. If you are playing at a higher resolution, like 1920x1080, you will probably have to run most of those games at reduced detail settings to get an acceptable framerate, especially Witcher 2 and Battlefield 3.
If you are playing at a higher resolution, you may want to look at something higher than the 6670. Though I can't make any recommendations without knowing more about your power supply (make, model, how many amps on the +12V rail). Your CPU is also rather slow, so a lot of the higher end cards would likely get bottlenecked by your CPU, especially in the more CPU heavy titles (BF3, StarCraft II).