For now(& for the time to come) PCI-E.For the very simple reason that it can push more bandwidth at a faster rate with today's modern day video cards & also because AGP is almost being phased out now.If you check then none on the 8 series cards fall in AGP catergory.
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"Beneath this mask there is more than flesh. Beneath this mask there is an idea, Mr. Creedy, and ideas are bulletproof. "
V for Vendetta
Well , PCIe excells only with SLi or CF ... for a single card performance , the AGP cards are no less performing than their PCIe counterparts .. but PCIe is more future compatible than AGP .. overall , PCIe is the better choice ..