Short answer first ^_^:
ATI provides the better value for your particular purchase. Furthermore, for the generation of cards you listed, ATI dominates that architecture span to such an extent that I woudn't even consider the NVidia products.
I would recommend buying a card from http://www.newegg.com as they are competitive in price, and I haven't ever had a problem when ordering or returning a product from/to them.
Longer answer:
The concerns voiced by various posters (and yourself) concerning ATI drivers may have been relevant five years ago (I can personally attest to this), but not anymore (I can also personally attest to this).
Since their purchase of ArtX in 2000, ATI has arguably produced a superior GPU architecture the past few years. A simple examination of the process migrations (those little 130 nanometer numbers that everyone loves to quote even though they rarely know what the number actually means) shows that ATI has a more mature architecture at this point.
Consider that the three big next generation console manufacturers (Nintendo, Sony, and Microsoft) will all be using ATI GPUs, perhaps the largest indictment of NVidia's current architecture.
I'm not going to get very technical here, as I don't think that's what you want. I don't like Tom's Hardware for a few reasons, so if you wanted to do some more research, I would suggest the following sites:
http://www.anandtech.com
http://www.arstechnica.com
http://www.sharkyextreme.com
Specifically, the system guides might give you some useful comparisons for your type of purchase.
If you want to get technical, then I would suggest you read some of the features on AnandTech, then when you're comfortable with those, steer yourself to the following site, which far and away is the best for in-depth technical articles on computer technology.
http://www.aceshardware.com
As to the poster who claimed ATI takes shortcuts in their texture filtering, I doubt very much he understands what texture filtering is in the first place. Second, I would caution you largely to ignore his comments, as not only are they incorrect, they are completely irrelevant to your intended purchase and use.
Finally, you'll be able to play FFXI quite happily with any of those cards. ^_^