Are they the same price? If so, the Conroe is better. But there wouldn't be a whole lot of difference.
save yourself a little cash and get a 7900gs instead of the 8x series and spend the savings on ddr2-800
Don't spend more on DDR2-800 for the Conroe, at stock speeds there is no difference between 800 and 533, and the 775Dual-VSTA is a shabby overclocker. Even DDR2 667 is faster than you'll ever get the 775Dual-VSTA to go.