cc by sa is probably the most common variation used on both wikipedia and commons it is also in a way compatible with the gfdl used by default any limitations might disqualify it as free enough for wikipedia most notably free images here must allow for commercial reuse again for gfdl compatibility i presume so nc is out of the question though i'm not an expert on this you can check the upload wizard follow the own work path and see the available choices though you might also seriously consider uploading the image to commons instead to allow wider use