The higher number models carry a higher price, and faster RAM and core clock. Other than that, I believe they are exactly the same in what features they are able to support.
Let your wallet decide how much you can spend, and then get the card that best suites your taste. From what I've read, there is minimal difference between brands of the video cards with the same chipset. Personally, I like Gainward's cards, but there are other good brands out there too, I've just not had much experience with them