Generally speaking the 512MB GDDR5 is going to be better. The GT 440 is not fast enough to really benefit from having 1GB of RAM. The faster memory on the GDDR5 card will give you better gaming performance. If you are running high resolutions, you would want at least 1GB of memory for gaming, but the GT 440 simply isn't powerful enough for high res gaming anyway so that point is pretty much irrelevant.
If you're not gaming it really won't make a difference either way. Basic desktop applications and video playback aren't effected by the amount of memory or memory speed on the cards available these days, either will be sufficient.
Okay thanks for your help. It'll be for some light gaming such as WoW but nothing that has major graphics. Just out of curiosity, would it be able to run Skyrim on low graphic quality? It's not going to be used for playing Skyrim, I was just wondering really to give me some idea of how much it can take.
Depends on what resolution you are running. At a lower resolution like 1280x1024 or 1366x768 or something like that the GDDR5 version could probably do medium in Skyrim. Resolutions higher than that you may have to turn it down to low. The 440 isn't a high end gaming card, it will run most titles, but you will have to turn details down as your resolution gets higher.