i really can't understand why anyone buys the 7800 or 7900 over the Ati 1900 xtx.. it just a better card all round and it will last a lot longer.. but if people feel like supporting a brand name that is not as good as another brand and pay around the same price then good on you.. me i always want the best now and for the future and if it was the 7900 i would have got it..!! and if you are looking for something a bit cheaper then.. 1900xt.
Hm... "best card?" Apparently, there's no clearcut winner this time, even though the X1900 cards are cheaper. True, I wouldn't buy a 7800GTX now with the 7900GT/GTX and X1900 cards available, but I wouldn't give the nod to either card.
First, look at the scores. Even on this website, the scores were pretty evenly matched. Go to Gamespot's comparison of SLi 7900GTx and Crossfire X1900XTX, and you'll see that the SLi cards won 3 of 5 tests. In one of the tests that the 7900GTX SLi card lost, they bested the ATi X1900XTX Crossfire in that test (SM3/HDR)... until FSAA was turned on. Yes, you can't run HDR and FSAA together on an nVidia card, but until Bethesda releases a patch, you can't run them together in TES:Oblvion, even with the X1900XTX. That means the two effects are also software-dependent (unless you own a 360).
And that leads to another reason why one would prefer the 7900GTX: SLi. So many people bought SLi mobos over the last year. And while mobos are "cheap", I'm sure many of those people aren't willing to gut their whole PC just to upgrade their videocards (assuming that they can afford to!). If they bought them from a PC manufacturer, for instance, they might just rip the old cards out and replace them with new ones, not knowing even how to upgrade the mobo.
And a 3rd reason: the 7900GTX cards require less power and therefore generate less heat. I also understand that the fans are quieter.
Of course, these reasons aren't valid across the board, given the heady number of manufacturers who are making these cards. But I was planning on upgrading my 7800GTX 256mb card next month (I bought it back in August for $500 and have no regrets -- it's done me very well), and now I'm going to wait. Both companies are producing cards that have their pros and cons right now. With the G80 and the R600 right around the corner, however, I'd like to see if either company can solve some of the issues that were raised with their last batch of cards.
Easy... x1900 supports more features and offers higher image quality. It either outperforms or matches the 7900GTX with the said bonuses.
And the Image Quality difference is there... and can easilly be spotted. Especially when High Quality AF is enabled.