Well that depends on what resolution you will be running and what games you are going to be playing if any and how many monitors you will be running.
So if you are using 1920 x 1200 resolution or higher and/or using a more than one monitor and/or playing the BF3 I would the one with 2GB of Vram.
If you plan on not upgrading for a few years and plan on getting games like BF3 in the fucture then get the one with the 2 GB of Vram. But the XFX one has a better track record with warraties and is a good card.
So unless you plan on not doing any of what I have stated then get the XFX one. The memory clocks can be turned up or down with programs like MSI Afterburner so you can OC them or not.
Anyway I hope this has helped a little and If you have any more questions feel free to ask. Good luck to you.
Honestly I would just get whatever one is cheapest. Even if the OP is going to run at 1920x1080, the card is going to run out of juice before it can really utilize the memory of the card. If you are going to keep it for a short while that is.
Although, I would really take into account what the other two have mentioned if you are going to keep it for a while. Little things are going to make a bigger difference down the road.