It depends a bit on what you're after. Currently the WD AAKS drives are the fastest 500Gb HDDs, they're a fraction quicker than the Seagate 7200.10s.
However if you're looking to do this in the next few days it's probably worth checking out the Hitachi T7K500s that are on special this week, they're around the same speed as the Seagates, maybe a shade slower.