First of all, laptop video cards are usually not as good as desktop video cards.
ATI doesn't have high end card that performs as good as nvidia for laptops. The best laptop card for ATI is X1800 which can't outperform the old geforce GO 7800. Also the mid ranged video cards like X1600 doesn't perform as good as 7600. The only think that ATI can compete with nvidia is with the low end cards.
But if you want to buy high end or mid ranged card then it is better to get a video card from nvidia
The best video card for laptop is nVidia Geforce GO 7950GTX, and it should run any game on high setting. Also, you can have two 7950GTX in SLI for laptops which will let you to run any game on very high resolution. Personally, I think one 7950GTX is more than enough, and SLI is just waste of money.
7950GTX is too expensive, so if you can't afford it then you should have look on 7900GTX, 7900GS, or 7600.