Either of the drives you listed are great drives. The Western Digital Caviar Black is an excellent drive for the price as is the Seagate Barracuda. I've owned both Seagate and WD drives and can say they are both quality performers. In general, a drive with a large cache is quicker in retrieving frequently used data than the same drive with a smaller cache.
After looking at the prices, I would suggest getting the Seagate from Newegg. It'll be cheaper in the long run as it has free shipping.