Which card is more powerful?

The PCi-e card is better because the agp bus on motherboards is the slower then the PCi-e bus on a supported motherboard. The whole reason that the industry switched to PCI-express is that the new CPU's can process much faster then the old agp bus can keep up with so PCI-e was created to take advantage of this. Besides with the new DX-10 models that vista runs you dont want to run a agp board anyway