1. Pay attention to the 3GB or 6GB version. If possible get the 6GB version due to the other differences, VRAM size is not the main issue.
2. Only take from trusted brands: MSI, ASUS, Gigabyte, eVGA or KFA2
3. Pay more attention to the cooling solution than factory OC. Usually, factory OC does related to cooling factor but remember, you can easily OC your GPU on your own. No need to pay all out only for some extra few mhz. The cooling is more important.
4. after you narrowed down to only few choices, take the cheapest among them.