Western Digital WD5000KS Caviar SE16 - 500 GB
Western Digital's WD5000KS Caviar SE (standing for Special Edition) competes directly against Samsung's Spinpoint T166, which also offers 7,200 RPM and 16 MB cache memory. Its transfer rates are no match for the Samsung drive, but the access time and I/O performance is clearly quicker. According to the datasheets, the WD5000KS also requires less energy than the Samsung T166, but the Hitachi T7K500 is even more efficient.
The Western Digital product Website says that the drives reach a Windows Vista Experience Index score of 5.9, which is the maximum today. But the Website doesn't mention the drive's configuration (four platters) nor the MTBF number (Mean-Time Between Failures). Western Digital offers a three-year warranty, and compared to Samsung it, produces most of the hard drive components itself (including wafers and sliders) if you feel this could have an influence on your buying decision.
The WD5000KS is slightly more expensive than the Samsung Spinpoint T166, but the difference is small enough to be negligible. Both are excellent drives; WD has the better reputation and its hard drive has a quicker access time, but the Samsung drive has higher data density and throughput.