Better to get now? Depends on how much you're willing to spend. PCX is going to be (performance-wise) much better both now and later compared to AGP, but it's also going to be quite a bit more expensive. PCX with a proper GPU (6800 Ultra or 2 of them in SLI, anyone?) would make for an "awesome" gaming and video editing machine, not just a great one. If you don't wanna spend the amounts needed to go PCX (costs for mobo and video card/cards) then AGP with one of the newer high end cards would definitely still make for a great gaming and video editing machine both now and a decent way into the future (couple of years... max).
:beer: