The Palit ATI has a 350mhz core and 500mhz memory while the Power Color has a 100mhz core and 2ghz memory. The GigaByte says it has DVI but it's really VGA II. Also it has a 40mhz core but it's dual-core so it's essientially 80mhz.
I would get the GigaByte one because it comes in a blue box which is pretty.
Also the Palit comes with 3 fans and 2 heatsinks so it's nice and quiet.