If money was no object, the X800XT of course.
However, back in the real world, I'm going to have to see how retail X800pro / 6800GT boards & drivers compare. Judging from the benchies from different sites, they're aboot equal across the board performance-wise, with the X800pro taking the biggest lead in Far Cry & Painkiller. Interesting that xbitlabs tests on the HL2 beta put nVidia in the lead now though - don't know if that was still partial precision.
I'm leaning towards the GT since I plan on keeping it at least a couple of years (still got my GF2!) and I figure SM3.0 will come in handy by then if the GT has the horsepower to really use it when it's needed. Although, the X800pro will be available sooner and I'm getting tired of waiting, and having to hijack my mate's PC to play Far Cry and Painkiller.