I would say it depends where you read the article. If you go to articles and find the article that's called 4870 better than GTX260 so will see the exact same thing, just in the opposite way, where 4870 come as a better choice so I really think in this question will answer, which one you like more ATI or nVidia.
You wouldn't be able to notice the difference between the two ingame.. just buy whatever's cheapest/floats ur boat
If you can't decide GTX260 216 or 4870 1Gb check this!!