AGP for sure if you can do it. From Tom's Hardware
http://www.tomshardware.com/2006/07/24/graphics_beginners/index.html
PCI
PCI stands for Peripheral Components Interconnect. It is a 32 bit wide bus that runs at 33 MHz, delivering a bandwidth of 133 MB/s. The PCI interface replaced ISA and its extensions (VL - Vesa Local Bus) in the 1990s, with the benefit of much higher bandwidth. PCI is the current standard for most computer add-in cards, but contemporary graphics cards no longer use PCI, as they have long since moved on to the AGP (and PCI Express) interface.
In many cases, however, computers from large manufacturers will come without an AGP or PCI Express port for future graphics expansion. In order to upgrade the graphics card on these machines, the only option is a video card with a PCI interface, but these are scarce, overpriced and have low performance.
AGP
AGP is a high-bandwidth interface designed specifically for graphics cards. It was based on the PCI rev. 2.1 specification. Unlike PCI, which is a shared bus, AGP is dedicated to one device. This allowed AGP to have numerous advantages over PCI such as directly read/write capabilities with the system memory, de-multiplexing or simplification in the organization and transfer of data, and increase clock speeds.
AGP has gone through three major revisions, with the newest being AGP 8x at 2,1 GB/s, meaning that it is eight times faster than the initial AGP standard at 266 MB/s (32 bit, 66 MHz). AGP is being replaced by the PCI Express interface on new motherboards, but AGP 8x (and even AGP 4x) still offer sufficient bandwidth for contemporary video cards. All AGP 8x cards will work in both AGP 4x and AGP 8x slots.
