It will ultimately depend on the model drive you choose, however as an overall answer, I would say that western digital makes high quality fast drives at a good price, I use mostly all western digital drives for the computers i build using SATA and SATAII. I also have had good experiences with seagate with their server drives, I am not sure if the quality of those drives also carry over to their desktop line. Are you looking for a high performance drive (10K RPM) or a standard desktop drive?
In my experience, WD drives last forever with reasonable care. I have several WD drives in older computers, some of which are 10 years old, and they continue to run flawlessly. In the event that a drive does fail (couple of office machines over the years), WD has a no hassles RMA policy provided, of course, that the drive is still under warranty.
The 3-platter 500GB Caviar SE16 is currently the fastest 500GB drive on the market, and it's priced under $150 from New Egg.
I pick D i have always gotten Western Digital drives and the first drives i bought from them still work great.
Only had one fail on me but it was dropped in the past so that prob contributed to its failure but still lasted a long time.
i've actually suspected if wd product varies from country to country. years ago my wd died exactly end of the 1 year and seller want extra money for new one but i did not give anything. many years later i did same mistake and bought wd again and never work so i sent it back.i'd same problem with samsung two hdd.they stopped 1 year later.i don't know maybe just my luck...
i used quantum,maxtor hdd's then later and now seagate hdd's.until now i don't have any trouble with seagate.