Currently, nVIDIA produces what most believe is the "best" video card for gaming purposes, the 7800GTX - KO (an overclocked and slightly different version of the 7800GTX). eVGA manufactures the best version of this card, which comes in several different colors and can ve found on newegg.com.
ATI's flagship gaming card is currently the x850XT Platinum. It outperforms any of the nVIDIA GeForce 6 series cards, including the 512 MB 6800. It falls well short of the 7800GTX however, in both performance and features.
Although I cannot tell you weather ATI is better than nVIDIA or vice-versa, I can say that nVIDIA's GeForce 6 and 7 series cards are much more reliable than the 5 series cards. After its FX5950 flop, (the ATI 9800 wes a MUCH better card), nVIDIA "got its act together" and began to turn out competitve products.
Both nVIDIA and ATI usually produce reliable products.
My advice: go with a GeForce 7-series card from eVGA. Thier products almost always are reliable, and deliver great performance.
By the way, do you have PCI express? Before you buy a new video card, make sure you do. I think the FX 5200 was an AGP 8x card.
Also, could you post your system specs?
Regards,